Speakers and room acoustics have the most effect on the quality of the sound you'll hear. Electronics are a distant third, although room equalization software can make a big difference. Don't forget that you'll need sound treatments (absorbers and diffusers) on the interior walls. Otherwise the audio reflections off those hard surfaces will be almost painful. What's the budget? A ballpark figure is needed in order to make reasonable suggestions. A traditional recommendation is to spend twice as much on speakers as on the electronics to drive them. You might want to consider two containers side-by-side with the adjoining walls removed. That probably would be too expensive, though.
That wasn't hostility. That was humor. 90" screen is too small. 110" will fit. You'll have to build a false wall and use acoustically transparent material. No, you wont have to do the entire thing in AT material. And you can build a door.
And that small of a budget for audio? How much are you budgeting for acoustical panels? http://www.crutchfield.com/S-wzp3IONthGK/p_15450100/Dynamat-Dynil.html How much for the projector? I assume ceiling mounting and "everything" fits this dimension...you can buy darn near any projector you want.