Some thoughts:
I have a large (23x25) dedicated home theater with a 123" screen. I'm using a Sony G90U and running all of my sources through a Faroudja 5000. Here's what I've learned.
1. As Glenfihi said, wire your Projector and amps on independant circuits. The sound won't be affected as much as the display -- very sensitive to noise.
2. I've found the the 123" screen is too big. If I were to do it again, I'd run a 110" or even a 100" screen.
3. If you do 2 rows of seating, you'll need to decide on whether you want to comprimise on the sweetspot, or have your sweetspot in the front row, at the expense of the back row.
4. If you have young children and like to watch action flicks at night, you need to take every measure to keep the bass from vibrating your house. My theater is in our attic, and we can feel the bass 3 floors down when we have the right movie showing -- doesn't help the kids sleep.
5. I've seen some stunning displays on 100" screens from the Runco single-chip DLP projector, and from the Runco 3-chip ($25K) on a 110" screen.
6. In that big a room, it's less neccesary to place the center channel speaker behind the screen, but you may want to experiment.
7. I used to run seperate amps, and I found it a bit tedious to get all of the sound synched up properly. Now I run a Mac MHT-200, and the sound is awesome.
8. Crestron, Elan and AMX are really intended for controlling whole-house automation. I think they might be a bit of overkill for just operating a theater, and you'll be paying ~ $10K for a theater controller. I think there are quite a few sub-$2k (including programming) options that will do everything you want.
9. Use 2 subwoofers to really add punch to the whole room.
10. Mount your surrounds well above your ears (when sitting) and use dipole speakers. The sound that comes out of the rear and surround speakers is 99% ambient and effects, and you just want it to fill the air behind your head, not be directed at your ears.
11. Most important!! Hire a pro to calibrate and fine-tune your picture and sound. And recalibrate the picture every year or so. This has made a huge difference in my theater.
12. I'm not a huge cable freak, and have had great success using both Tara RSC and Monster for my sound (Monster being 1/4 the price). But I have learned that you want to use the best cable you can afford to connect your Processor to your display.
13. My $6K+ Mac receiver has no HDMI or DVI inputs. Your new sources for satellite and broadcast media will need these. Be sure to buy a processor that has multiple hi-def inputs and at least 2 hi-def outputs.
14. You may want to mount a plasma or other display for casual viewing. I'm not sure that you want to fire up your theater to catch the late-night scores or to watch an NTSC broadcast for 30 minutes.
that's enough fo now.