Before buying equipment you might consider doing a room build that isolates it from the rest of the house acoustically. Usually means floating walls, ceiling, and floor if not on concrete (bottom level room). Also isolating from the house HVAC ducts that transmit sound everywhere; I used a Fujitsu minisplit unit so the media room is on its own heating/cooling system. You'll also need an external air source for fresh air; I did not do anything special with that since I live in a quiet area with plenty of space between houses (2.5-acre lots). I used Kiinetics Iso-Clips plus 6" mineral wool for the walls and ceiling and the contractors had no problem. After all that I can crank the stereo at 1 AM while my kid is sleeping in the room on the other side of the wall.
Pre-wiring is pulling wires for speakers to where you think they'll be mounted. It sometimes includes outlet boxes. Can also include network wiring, cable wiring, etc. I personally don't pre-wire speakers, as I always seem to need them someplace a little different than I thought, so I just run wires along the floor or ceiling. I did prewire for cable, and included a couple of 20-A drops so I had plenty of power to the media room. I also included a couple of switched outlets for floor lights. I ended up with a single standard 15-A run for lights and "back" outlets plus two 20-A drops along the front wall for all the HT stuff. You may also want to prewire for a ceiling-mounted projector (power and interconnect wiring). You'll need to decide what you want and where.
You might want to hook up with a local audio shop to help design the room and wiring.
Can't help on the speakers. I have Rythmik subs and love them but there are many choices. It's a good-sized room; for HT a couple of FV15's should work nicely.
HTH - Don
"After silence, that which best expresses the inexpressible, is music" - Aldous Huxley