So sorry, don’t know why it didn’t upload with the post!

You probably would want to post in the Lawn Care (or whatever they call it) forum. And possibly in the regional forum that applies to NC, as both those would be more specifically related to your questions than would Landscape Design. You said you put down pre-emergent, but didn't mention applying any fertilizer. Lawns need it for greenup & growth, especially when irrigation systems are washing nitrogen out of the soil on an ongoing basis. Likely, you'll need pre-emerge 2x per year; there are winter weeds as well as summer ones. A post-emergent herbicide for centipede lawns (you'll need to check labels) will probably help you out with any broadleaved weeds. For grassy weeds you may need to dig them out (use a spading fork, not a shovel) and be sure to prevent their reoccurence in the future.

The black thingy has a black cap with a rectangular hole to accommodate the downspout. You should be able to slide the cap upward on the downspout to possibly allow cleaning any leaves in the black thingy. Also, if you remove one of the screws thru the metal strap shown in your photo above the thingy, you may actually be able to get the downspout out of the thingy.

You don't need phosphorous unless you have a current soil chemistry test showing low phosphorous. Since this is new construction, you might ask your neighbors to see if anyone else has gotten a good soil test, because your soil is going to be identical to everyone else's. The best place in the US to get a soil test is Logan Labs in Ohio. Why is it the best? Because, for $25 they do more tests than other labs, the tests are more repeatable than other labs (meaning you'll get the same results as your neighbors' sending in the same soil), and the test is more reliable (meaning more accurate results than other labs). There is another garden forum where they sent soil samples to labs across the country. Two labs stood head and shoulders above the university labs and other private labs. Those labs are Logan Labs and UMASS. If you aren't an expert soil chemistry analyst, you can post your LL results to another forum and they will read it for you. They will tell you what to use, when, how much, how often, and where to get the materials. If you Google soil test, dchall_san_antonio, and morpheuspa, you'll find the forum. They have all the instructions for digging up the soil and how to get it done. As for your soil not being the best, you're going to make it the best starting with the soil test and your care of the soil. Just leveling and putting down the sod is a perfect start. Even builder grade sod is light years better than your parent's lawn, for example. You do not necessarily need to aerate it in October. I realize many, many people will tell you that, but that's old technology. Research on athletic fields and golf courses shows that using a surfactant is equally good as core aerating for keeping the soil open. Personally I think surfactants are far superior to core aeration. The golf courses spend a ton on surfactants, but you can get away with using shampoo. I use baby shampoo, but you can use anything you can get from Dollar Tree as long as you can see through the bottle. The shampoo needs to be clear and not cloudy with conditioners. The application rate is 3 ounces (or more) per 1,000 square feet. You can apply it any day of the year, or every day of the year. It won't hurt anything. I applied it once in 2012 and have not needed to repeat. Here are the basics of lawn care for a novice. You may as well get the full deal so you can have something to refer to. There are three main elements. Those are, in order of importance, watering, mowing, and fertilizing. Minor elements are weed and pest control. Watering: Deep and infrequent is the mantra for watering a mature lawn. Deep means 1 inch all at one time. You can measure this using tuna or cat food cans. Put some cans around the yard and time how long it takes your sprinkler to fill all the cans. If one can takes forever, you may need to adjust the sprinkler. Remember the time it takes to fill the cans and that will be your watering time from now on. My oscillator sprinkler on full sweep, with my hose and water pressure, takes 8 hours to fill the cans. Your time will be different, so you have to check your sprinkler. Infrequent refers to how often you water. For new sod you will need to water much less deep and much more often. Typically people water 3x per day for 5-10 minutes for the first two weeks until the sod is knit down to the underlying soil. If your sod is already knit down, then you can work your way up to the normal deep and infrequent. Infrequent refers to how often you water. There are many factors affecting how the soil dries out, but the main one is the air temperature. When temps are below 70 degrees F, you should deep water about once a month. When temps are between 70 and 80, deep water once every 3 weeks. When temps are between 80 and 90, water once every 2 weeks. When temps are in the 90s, water once a week. If you get temps above 100, water once every 5 days. Note that you never water for just a few minutes and you never water every day. If you water like this you'll avoid many weed issues (they need continual moisture to germinate), disease issues (fungal diseases need continual moisture), and the grass will develop deeper roots that withstand the summer heat and dry spells. If it rains, take that into account when timing your next irrigation. For my area in Texas, and for most years, I don't have to water until July because we typically get multiday rain events in late May. Watch the grass and let it tell you when to water. Mowing: Mulch mow the grass at or near the mower's highest setting. Grass grows at the same rate no matter how high/low you mow it. Mowing high has the benefits of looking great most of the time, it provides more shade to the soil keeping it cooler, and it provides shade covering weed seeds which need sunlight to germinate. Mulching returns the clippings to the soil like an organic fertilizer would. If you see piles of grass when you mow, then mow over the piles to scatter the shreds of grass around. You don't want clumps of grass sitting on top of the grass. Fertilizing: First fertilizer of spring should come in late spring, not early spring. You'll have to turn your eyes and ears off during the commercials on TV and don't listen to the hardware store hucksters trying to sell seed and fertilizer in February. Memorial Day is a good day for fertilizer in your area. If you apply in March you'll need it again in late May anyway, and you don't need it in March, so save yourself the time/money. In the spring the grass will tend to leap out of the ground no matter what you do. If you fertilize early it will leap faster requiring more mowing. Plus the grass burns itself out nutritionally, so just don't do it early. Use a real fertilizer and not a weed and feed product. Morpheuspa will come by to help you pick a fertilizer. I'll give you a heads up, though, he's an organic kind of guy (as am I), so open your mind to other possibilities. Fertilize again on Labor Day and again around Thanksgiving. Weed control: Apply a preemergent herbicide when the forsythia start to bloom in your neighborhood. That means buy the preemergent before they start to bloom so you're ready. Again, morph can help you pick one. For weeds that slip through the preemergent barrier, you can spot spray those in mid April with a product like Weed b Gon or Weed b Gon Chickweed, Clover, and Oxalis Killer. There are some specialty herbicides for special weeds and grassy weeds. If you get a grass or plant that does not go away with the WBG products, take pictures and post them here. That's what the forum is for. If you are doing the watering and mowing properly, you should have very minimal weed pressure even if your yard backs up to a field of weeds. For example one writer here reported that his neighbor's crab grass came to a complete stop at his border, because he was mowing his grass high. Crabgrass must have full sun, so tall grass is an excellent control against it. Insect control: Don't worry about insects unless and until you see damage to your lawn. There are bazillions of insects that live in lawns and cause no damage at all. I can't cover them all in one go, so if you think you have an insect problem in the summer, please write back. Disease control: Sometimes Mother Nature throws a curve and blesses you with enough rain to cause regional disease issues. If you have an active disease, then consider using a fungicide. Otherwise, do not use fungicides because you get scared that you might get a disease. Just because your neighbor gets a disease does not mean you will.