First, I'd stay away from acoustical tiles on the ceiling, definitely! Your small acoustic space (and that's still small) needs more diffusion, not absorption in the mid/high's, with the limited bass absorption pressent in your room, Basically, it's going to be too warm sounding, and a bit dead. YOu do however need to treat ceiling reflections between you and speakers, unless you either sit closer, or use more controlled dispersion (vetical) speaker designs, which the Maggies are.
Still, I'd NOT use the Maggies with your receiver, as Maggies are low efficiency, low sensitivity, limited in dynamics(not what good HT needs), etc.
If I knew your receiver, I could make more solid recommendations for cheap.
However, in general, lower model KLipsch horn speakers are very dynamic, easy to driver, controlled focused, and make great home theater speakers for little! They also make acoustics more managable with their controlled dispersion.
In short, the dynamics will be 3x's stronger with something like Klipsch SB-1's or RB-25's or whatever, yes! And this IS an HT system, right? These speakers are also pretty clear and uncolred from my recollection.
As for the PJ, I'd go with cheap DLP for now, or a Sony LCD S51(best black level of LCD's out, marginally acceptable).
However, my first choice is the bargain on "used" CRT projectors right now, either mounted on ceiling in a box, or in an enclosure between the front seats on the floor. This IS THE BEST PICTURE you'll ever get for any reasonable money, period!
Case in point: You can get an 8" CRT pj for around $2500 with minty tubes, that will last you years, and give you a world class picture for as cheap as possible.
If it where my money, and I was using your receiver, I'd go used CRT, maybe Barco 801 or better Sony G70 on the high end for $3500 range used. OTherwise, I'd look into NEC PG9200 or whatever. World class pics here folks
Down side is these are bulky, and need tweaking.
As for back door on back wall, you can do 6.1 set up just fine there.
Actually, I think 7.1 setups are recommended with two speakers right next to each other in teh middle back anyway. So this should work.
Good luck