That was quite a few questions.
1. HD screens are the only way I recommend people to go, even if your viewing is limited now, an off-air receiver might pick up 5-10 channels for you later this year if you want one.
2. DirecTV is all digital which means it's quality is far better than the analog cable channels - comparible to digital cable channels. It looks good on a projector as long as the image isn't to big and you aren't overly critical of it.
3. Movies on DVD will blow you away! Especially if teamed with good sound.
4. Front projection absolutely requires light control. If you have a lot of light in the room, or have a hard time removing most of the light from the room, then front projection is not the way to go as your primary viewing source. Bulbs burn out much faster than they do for rear projection (size/brightness issues).
I've said this in other posts, but I used my front projection in my family room as my primary viewing source for about a year. I blew a bulb at about 9 months - $350.00 to replace. That's about 500 bucks a year in bulb costs and when I moved into my new home, the image was TOTALLY washed out during the daytime. Not enough light control. So, in 5-6 years I would drop about 3 grand on bulbs and I really wasn't enjoying the projector during the daytime. Fine, instead of 3 grand in expenses in upcoming years, I took the money and bought a 50" plasma. Now the screen comes down in front of the plasma at nights for HD and DVD viewing, and is up during the day for normal TV/HD/DVD watching.
Best decision I ever made as far as I'm concerned and my wife is very happy with the plasma.