In my opinion a regular TV can't give you the same theater experience as a projector "big" screen can give you. It is really up to what you want. In most basements you can control the lighting, but you normally would not have all the lights on and windows open when your watching TV/Movies, using a projector. We never go to the theaters anymore. We have a walkout basement and it is just fine, the theater area is over to one side of the room. When I have Nascar or Superbowl parties, we leave the lights off in the HT area, but shot pool across the room and it works fine. My room is very large though.
I built my own screen, but you can also pay a lot more and purchase from a mfg. Some even use a paint formula on a wall with no texture.
In regards to wiring, make sure you run sub coax runs to all wall locations, even if you don't use them all at first. The sub is the hardest speaker to place to get great performance and you don't want to have to run cables around your floor trim after the fact once the walls are done.
