1) Pump should work fine. But, that will depend on the look you want for your waterfall.

2) A pressurized filter would be great for your situation. Our (Ultima II 4000) filter has run 24/7 for five years with no problems. They take up little room and require very little maintenance - maybe 20 minutes a month. Match size of filter with your pump.

3) You will probably want a 60 watt UV sterilizer.

4) Good idea to have the bottom drain.

5) Filter should be very close to pump. You might look into a pump with built in strainer basket. Then water should go from bottom drain to strainer basket/pump then to filter to UV light to waterfall.

6) Skimmer is nice if you have airborne debris in the area. Our area is clean and we do not have skimmer.

Thanks for the info. To clarify one item, is it okay to have the pump and filter down at the pond end? Will the output of the filter be able to make it 50ft up to the waterfall? I always assumed that the pump would operate better pulling the water up to the falls, but instead can it push the water through the filter and then up?

The pump and filter should be as close to the pond as practical. Also, pump should be right at pond level if possible. I have the intake of my pump right at pond level and have a 40' throw to top of my falls. Important to keep in mind to have as few number of angles in plumbing throughout your system. Also, one of the best things I remembered for our pond is to have a "winter bypass" of the falls. With a turn of a valve I can put the water directly back into the pond and bypass the falls. This allows, 1) work on the falls without disrupting the flow/circulation/filtration, and 2) if there is winter freezing, or other winter problems, the falls can be shut down and still have circulation.

Our setup:

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We have a 2500 gravity fed DIY system with 3 rubbermaid type tubs daisy chained together. AS the koi grew we added more tubs....Our skimmer is located
under a small dock and only used in early spring to catch the floating pollen from the trees. We also have a 200 gallon biological pond that all the water passes through
getting scrubbed in it's path before entering the main pond again. The biological pond can be added later if you choose to do so.
You can read about it on our Pond Plans and Diagrams --on our pond website.
Built with adequate filtration, there is no need for a uv light. We don't use one, and don't use chemicals as well. Just keeping the filter pads clean gives us a sparkling clear pond all the time.

Here is a link that might be useful: Pond Plans and Diagrams.

We have about the same size system as you, Chris, & Cliff/Joann, 2500 glns, 12 ft. head, not quite as long a run, although we use a skimmer with a small filter, not the bottom drain. Our falls drop the water into a steam bed near an upper pool, then water falls over a dividing falls between the small upper pool and the larger lower pool.

The skimmer housing located at the end of the water's run (lower pool) has the pump in the bottom. The only way I've ever seen it done was to PUSH water from the pump up to the Bio-Filter. We didn't use a stand alone prefilter because we just didn't think both a mechanical filter and a bio-filter, a stand-alone bio-filter, was necessary, especially with no koi planned.

IMO if you are using a bio-mech filter wouldn't you want to go with the manufacturers recommendation on sizing and pumping through it? I would think there might be an issue or two with how well it filters if you pump to fast or too slow; I could see there being a wide range available though (re: flow rate).

We use an Atlantic 1500 BF (wish it was bigger) has plenty of room for the filter media at the bottom where the water typically enters the open-air chamber. Our bare-root and gravel-filled meshpots go on top of the filter media. We actually have two pumps in our skimmer box: one goes to the bio-falls; the other one goes to a discharge pipe right below the weir and creates a rapids effect... gives us a way of changing up the rate of water into our stream bed by turning on and off the rapids pump.