9 fish in a 20g is a lot. I think your best bet is to get your rock and inverts out and hypo the DT and your QT won't really cycle at all if you fill it with your live rock
don't waste your money on ich meds they don't work. You could move your rock and inverts to the 20 and hypo the DT. But you should get the QT up as soon as possible also you really don't need sand in the QT
You don't necessarily have to keep it out of direct sunlight if you have a way to keep the temperature stable. as far as glass or acrylic goes they say acrylic is clearer but it scratches easier and costs more.
The Kelvin value isn't really that important when choosing lights but you do want them somewhere between 8000K and 14000K. What you really want is the par and pur value of the light
You should get a bigger tank if you can but if not go with a 40g breeder instead of a tall so there's more foot print. Forget the prime treated tap water still isnt good enough get your self a RO/DI unit. You don't really need the skimmer unless your going for a reef. Your perfectly fine only...