Congratulations! Your first pond is exciting. Have fun! You will hear different opinions and mine is just one. I am not an expert. My own experience has led me to avoid buying fish from the usual chains/pet stores. I had a bad experience with my first gift of "feeder" fish from a coworker that were all died of parasites. It was heart breaking. After that I located a smaller local place that sold a few pond supplies, plants and fish that used good quarantine practices and had a reputation for healthy fish. They were more expensive but I had completely drained and cleaned the pond to remove the parasites and started again and it was worth it. I have not lost a single fish to disease in the 7+ years since then. A lot people do seem to do ok with fish from other places but for me it wasn't worth it. I bought comets, I particularly like Sarasa comets, but Shubunkins are also popular and do well. Some fancier goldfish that can live in a pond are Ryukin and Fantails. I don't think they usually live quite as long as the comets but I have had one for 2-3 years so far.

Many people use a quarantine tank for new fish to make sure they are healthy before introducing them to the pond, but I found it easier to just find a good source for my fish that does that themselves. If you search for pond supplies in your area you are sure to turn up a good place or two nearby, even if it is not in your town. I found visiting pond suppliers in nearby towns to be fun and a great source of ideas.
Good luck with the pond and all the advise you will likely get. No matter which advise you choose to follow, you will have fun learning!

Thank you so much sue-ct I will definitely look into it. I appreciate the help :)

Here's the waterfall with a slight view of the depth.

Here is a top view of the size of the pond! How many fish do you guys think I can fit?

This pic is of one of the cracks that was dumping sand in from the inside of the pathway, you can still see some of the specks there on the liner. Does anyone know if I can patch them up with kitchen and sink glue? I don't remember what it's called in English but it's to stick sinks to the walls and keep leaks from happening.

And finally here's the filter with the description! I hope this helps everyone get a better picture of the situation! :)

By the way, your pond volume, depending on weather it is 2 1/2 feet or 3 feet deep is between 900-1100 gallons. That is a pretty good size. The number of fish you can put in here depends on the size of the fish. You need to leave room for them to grow. In a good environment they will likely also spawn and in a couple of years you may end up with many more (ask me how I know, lol). I would start with a just few at first, especially since your filter is new.

More or less I'd like to know the maximum so I can purchase no more than a fourth to an eighth of that amount. I think it be fun to be able to keep track of who's who for a while. and since you so kindly suggested I'll ask about the many more part... so, hoooow do you know?! XP

will the sand affect my pond life?
Yes, but probably not a lot. Certain kinds of life, animal and plant, will make the sand home if they make it to your pond.

What plant life should I add to feed my fish and welcome in other wildlife like frogs and dragonflies?
That really depends on the person. I like to add any plant I can and see how it does. It stays if I like it. That's how I learn. So for me I'd try any plant, and I'd try it different ways...in water, in soil, in sun, in shade, etc., to learn how it grows.

Duckweed is a plant fish will eat directly, but after they've eaten it all it's gone. So if you want an on going duckweed food source you have to protect some or easier imo is growing it in a separate shallow pond.

But a more important food source is all the life in a pond, mainly insects. They eat the plants and the fish eat the insects. So all plants really feed fish indirectly. Dead, rotting plant material feeds insects the best. But many people don't like that in their pond...so it's really best to decide what kind of pond you want...Wildlife Pond, Water Garden or Koi Pond. That determines how plants are used. You can try one and if you don't like it you can change to another pretty easy or some pond in between.

the water looks a little murky. (BONUS QUESTION) Is there any way to clean that up?
It's pretty simple to clear up water but only after you know what's causing it to be murky which is the complex part. There are lots of filters and methods to removing different things so the filter has to be matched to the stuff being removed.

One pretty universal murky clear is a 24/7 drip water change system. A drip emitter runs 24/7 into the pond and an overflow takes away the extra water.

I plan on heading over to a local park nearby and yanking out a couple of cattails and whatever else I find interesting, I highly doubt it's illegal and the poor little stream that leads to the enormous carp pond is choking with all the vegetation. (OH! I know that these plants will probably have other bacteria and algae and critters on or in it, is there any way to clean them without killing them?
There are chemical baths you can use, including chlorine and similar oxidizers. They aren't super effective imo. The question is do you want to do that or are all these critters something you want?

You see this goes back to deciding what kind of pond you want. A Koi Pond owner with thousands of dollars worth of koi would never allow any plant within 10' of their pond. Their focus is koi and the risk of pathogen form plant would be unacceptable.

At the other end of the pond spectrum a Wildlife Pond owner would welcome all those "pathogens". It's a matter of perspective. To these pond keepers "pathogen" is just another name for "life". That's what natural ponds are, life. Stuff killing and eating other stuff.

I want to make sure the plants are settled before getting fish, but I heard that a certain string? Algae is a pain to get rid of, does that grow in zone 9?)
You don't get rid of algae, you control it. Just like you weed a garden. Algae grows in all zones, from the poles to the equator. There are thousands of species.

...since I live in zone 9 in one of the cities that borders the Rio Grande, Does anyone have any recommendations for the type of plants I might want to scavenge for, how to transport and transplant them from the stream into my pond, and what no-no plants I should try to avoid?
Giant Reed, Arundo donax, is a spectacular plant you can probably find. It's an aggressive grower, makes bamboo look like Pussy Willow.

I don't believe there is such a thing as a no-no plant. They're plants, you're a human. I have to assume you can win any battle. Ponds are just like any garden. If you tend it you win. If you go away and come back in a year the plants win.

(If I find any I kind of want some duckweed... is this a no-no plant? Will keeping the growth at bay turn into an overwhelming hassle for my medium-small sized pond?)
Depends on how much hassle you consider keeping a pond is. For me it's a joy. And whether your fish.eat it.

I want goldfish!! I hear commits are really friendly, but what other species can I add? Can someone supply a list? Oh, and how many can I add? (I was thinking about 6-8 fish total)
Common, Comets, Shubunkin, Wakin. The fancy kinds can look a little out of place. I've had some of these because friends need to get rid of "pets" sometimes. They look a little odd to me when mixed with other kinds. Like when you feed them the others swim over fast and the Fantail seems to struggle to swim 10'. But the fancy ones seemed to do fine but need exact protection from streams, skimmers, etc., as they're not strong swimmers..

The Common, Comets and Shubunkin are also often crossed. Like a Comets and Shubunkin to get a Shubunkin with a long tail. Commons get the biggest, more than 12" and over 3' sometimes although these may be koi crosses.

(Even numbers so they can have a buddy system, but not like Nohas ark, they can only be friends!! No babies!!... okay maybe a few so I can add them to future smaller water features around the garden...)
You can post a sign explaining breeding rules but goldfish are either not very good readers or not very good rule followers (even worst than teenagers).

which leads me to the after thought question... Can different species of goldfish mate? I mean.. they are still goldfish...
Yes. When different kinds of goldfish breed the result is considered a goldfish too. Goldfish can also breed with koi.

I know that bottom feeders won't eat all the gunk that will eventually fill the bottom, (I can't blame them) But are there any fish that I can add that will eat the bottom pellets? (Like catfish maybe, or something cooler/cuter)
Pellets, as in sinking food pellets? Goldfish, koi, catfish, pretty much any fish will eat food on the bottom. There are terms like "bottom feeder" but that's just a general type thing. Like catfish will spend most of their time on the bottom but will eat food on the surface just like a goldfish or koi. And they will come a running when they see you just like goldfish and koi.

As for gunk...bacteria lives there, bugs too which eat the bacteria, bigger bugs that eat the smaller bugs and fish root around in there looking for bugs to eat. It's a whole cycle thing. Gunk on the pond bottom is basically soil, or stuff on it's way to becoming soil. Nothing removes it completely, just like nothing removes soil completely. Stuff lives in it, eats some growing in it, breaks it down into better and better soil (from a plant's perspective).

Oh, and is Walmart a smart place to buy these babies at? (I'm sure most are familiar with the store...) My only other option is PetCo... Are they a good option? I don't want to buy bad fish... but I would feel terrible if I had to take a fish back because it was sick or it got the others sick...
There not really anything like a "good" store to by goldfish.

Here's how it wroks. The store orders fish from a grower. The grower has a bunch of ponds with different kinds of fish. The grower puts a bunch of fish into a box and sends it to the store. The store dumps the box of fish into a big tank. An employee gets a net and scoops out a few of the the prettier fish and puts these into separate tanks. Like for instance some Shubunkins would go into a tank labeled "Shubunkin $4.95". And some orange and white Comets will often be labeled "Sarasa $4.95" even though they aren't actually Sarasa. The rest in the big tank are labeled "Feeder Goldfish 20 for $1".

When customers buy $4.95 fishes the clerks grab a net and scoop a few more nicer looking fish out of the feeder tank and into the $4.95 tanks. People just assume when they see 10 fish in a nice aquarium at eye level that they must be higher quality and healthier fish than the horrible feeder fish tank. It's just marketing and logistics.

You can often find very nice looking Shubunkins and Comets in the feeder tank. It just depends on what they get in. Growers don't care since it's just as easy to grow Commons or Comets or Shubunkins. They'll send whatever they have.

The fancy goldfish may be shipped in separate containers.

This is not to say all fish are healthy. In my experience 50% of feeder fish died in the first 24 hours. And in most stores they also don't last long either. Yes, you can quarantine them, you can treat them for parasites, etc. Depends on the kind of pond you want to keep. Most ponds I've had I only used feeder goldfish. Set up a quarantine tank and buy $10 worth of meds to treat $1 worth of fish...not me. I just put them into the pond and hope for the best. But that's me.

I do want to hand feed my fish. I know the risks of them getting hurt by other animals but I have 3 small dogs that scare away all cats and wild animals, but are really just yapping balls of harmless fur.
Pretty much all kinds of fish can be trained to be hand fed. Takes them a few times to get the idea but once they do they're trained.

The 3 small dogs...I hate to impugn the K9 reputation for diligence but all that yapping..yeah, that's mostly for your benefit. When you're not around and the Herons are having brunch the dogs are really unlikely to do more than blink at the carnage. The Herons aren't hurting anything...it's not like they're doing something horrible like squeezing a squeaky toy. They're just eating all of your fish. Big woop.

Now if the dogs happen to hear you at the front door then sure, they'll be off like a rocket to tear that Heron a new beak, jumping through plate glass windows, busting down doors, whatever it takes to impress you and keep those treats flowing.

Here is a top view of the size of the pond! How many fish do you guys think I can fit?
Really depends on how you keep the pond. If you test for ammonia and add bio filters you could keep, 30-100 goldfish. No testing ammonia and adding bio filters the 6-8 number seems about right.

This pic is of one of the cracks that was dumping sand in from the inside of the pathway, you can still see some of the specks there on the liner. Does anyone know if I can patch them up with kitchen and sink glue? I don't remember what it's called in English but it's to stick sinks to the walls and keep leaks from happening.
I'm guessing you're thinking of silicone caulk. That might reduce the flow of sand. There's lots of goops you can use, including mortar. Cram it in and hope for the best. But you might be up against a fundamental issue of the way it's built.

Sometimes (often) it's easier and cheaper in the long term to address the fundamental issue than trying to patch stuff. I do it all the time. I find nothing wrong with failure, only with not trying. Almost everything I do for the first time has to be redone. I call this learning. And I learn even more in tearing down a structure. I get to see how strong materials were, what worked and what didn't. Not suggesting you do this, but that's what I do and it has served me well.

...but I can say that it has UV filtration and according to the box it's adding biochemicals to the water that will help my pond later on. (What does that mean?)
It probably said something more like "enhance the biochemical processes". What this means is someone in marketing figured out putting stuff like that on the box sells more units. And it does...sell more units.

And finally here's the filter with the description! I hope this helps everyone get a better picture of the situation! :)
My latest rant on these types of products.

Haha Thanks for the advice waterbug_guy I found your impute very informative, clever, and funny. I will certainly look into the species you named and see what I can do about the sand problem. The type of pond I want I would say is somewhat like a koi pond, except it won't have any koi, and I won't burn a hole through my dad's wallet with expensive fixes. I'm hoping on keeping a couple of "pet" goldfish in there but I do want to invite different little water creatures to the pond, so long as they aren't endangering my main fish, (What I mean by main, are my originals, if they do happen to have frys later on, I won't mind those babies becoming a part of the food chain... unless they impress me like my super spy circus yapping dogs do!) And finally, I was already familiar with your filter rant and I found it very honest and educational. You wouldn't happen to be an educator would you? Because it would seem like a promising career for you!

Well at least in zone 9 you won't have to heat it all winter. I found after having the same 3 fish for 5 years, and they were goldfish in the 6-8 inch range, I was too attached to add fish that might have parasites and see what happened. Again, like water_bug said, what type of pond you want. I was still very upset when it became a heron snack, but at least it wasn't something I did. Even those who don't get attached might find keeping them alive in a heated outdoor pond for 5 New England winters too big of a time and monetary investment to take chances. It certainly would be easier if I could take water_bug's approach.

Check your local freecycle and Craig's list for plants and fish. Pond keepers always have extra :-)

I beg people to take water lilies. Water plants are very prolific.

Sorry, I thought you would fill in the blanks yourself, lol. I started out with 5 fish in a 300 gallon pond and I recently counted 13. I lost 2 due to one of them getting caught in the pump when the protective cage fell off, and one other that got caught in the filter, so I thought I would be down to 11. Nope. Just found 2 new babies less than 1 inch long. I have quite a few plants, water hyacinths that have gone crazy, as well as others, and I keep pulling out the water hyacinths but they still cover 75% of the surface. Plus the fish hide, especially the babies, and they move pretty fast, so it can be difficult to get an accurate count. But I never purposely put more than 5 in that pond. They reproduce without consulting me at all. I suspect yours will do the same.

You wouldn't happen to be an educator would you? Because it would seem like a promising career for you!
Nope. Just like thinking about ponds. It's an obsession.

If the pond is kept more like a Koi Pond, spotless, clear water and no plants, population increases is very unlikely. Newly hatched fry normally starve in these environments because there's almost no food for them. Newly hatched fry need very small critters to eat. At this stage fry are very small and very rarely (almost never) seen.

When a pond is kept more like a Water Garden, plants added, algae and muck is allowed to collect somewhat the food web grows. Fry can find more to eat and some have a better chance to survive.

When a pond is kept more like a Wildlife Pond, lots of plants, soil, water is allowed to be green, the food web can be greatest and many more fry can survive and get large enough to take man made food.