Hey OP,
I really love my projector, and I am still working on my Home Theater little by little.
I only own a projector. Which for the most part suites my needs, but there are times I wished I owned a TV. Like just for checking the news / weather real quick, where I know I wont be watching the video for very long, and there fore dont want to get the Projector started, etc. So if you have a TV, keep it.. .or downsizes just to have something you can watch stuff on for a short time.
Another thing, A screen can be built in expensively. YoYo wrote a thread about it and posted some links and pictures of what directions he followed to construct his. I built a screen using the same techniques he used, minus the border / masking system. Here is a link to YoYos screen thread:
http://forums.anandtech.com/showthread.php?t=3440
There's a link in there to an AVSforum thread with a lot of DIY screen material options.
Screen size
My Projector has a zoom and lens shift function on it. The zoom allows me to adjust picture size at a given distance. I have found this useful because my PJ is mounted on a shelf above my seating area and not to my ceiling. I found the zoom useful in determining the size of the screen I want based on my couchs location. Also, I have found that a bigger screen isnt always the best. Main reason being if you sit too close to a big screen you will have to pan your eyes/ head side to side order to see everything on the screen. I found this to be very annoying, especially when I play video games
movies not so much b/c of aspect ratios.
Cables
If the projector is mounted above you, behind you, etc, you will need long enough cables from your equipment to the projector. I have ordered my cables from
www.Monoprice.com. Make sure you plan where you want your gear in relationship to the projector. Another thing to consider is the route the cable(s) will take from your equipment to the projector. In my current apartment, I keep my receiver and other sources in a different room from my theater This freed up more space for me to install another couch or recliner in the room. In my old apartment everything was in one room, but I kept the equipment rack away from the seating area to cut down on noise generated by the equipment. My XBOX 360 can get pretty noisy when playing games.. that was the offending piece of equipment.
Sound
Well, you will need speakers of some kind and probably a receiver to drive them. Other can recommend that.
Light Control Room
.ie keep it dark. Black out curtains are very effective at doing just this. My GF made me curtains for my old apartment to cover my patio door. It was Black out cloth adheared to a sheet a fabric that she hemmed. It was mounted on a curtain rod. Block out all the light. The black out curtain was purchased at our local Jo Anns Fabric. It is also called Drapery Liner if you look for it on their website.. It was a simple and cost effective solution.
Shameless plug.. But I have thread here with a link in my sig to my theater build. Im uploading pictures when I can. Just got a camera the other day and figuring out the software and such to make pictures of reasonable sizes.
Also, look at
www.AVSForum.com. I have done a lot research using that site. If you can think of it, odds are there are multiple threads on it at AVS.