I was recommending 120" at 2.35:1......MAYBE 130" width at 2.35:1 if you really wanted to push the size. One of your constraints is going to be throw distance for the size of screen you want. MOST screen sizes should work, but something to keep your eye on. Projectorcentral.com has a great projection calculator just in case you weren't aware.
I don't see the primary seating on the back wall, but pulled forward at least 3 or 4 feet, which is yet another reason to stick with the smaller-ish 120" width screen based on viewing angles. Pulling the seating away from the rear wall also has huge acoustic benefits as well by getting a good 5' or more of separation between the surround speakers and the MLP.
It will be tough to reach all of your goals without gutting the room's drywall. Going to the studs will afford you the opportunity to run whatever electrical you wanted, easily run speaker wires, add clips / channel for decoupling and then add back two layers of 5/8" drywall with Green Glue. It will also give you the chance to expose the framing around the door so you could then remove the french doors and go down to a single, solid soundproof door with Zero International seals all around. Yes, the theater would be slightly asymmetrical, but if the seating is aligned with the center of the screen, all should be good with the right setup and calibration.
If you are thinking Atmos, you'll definitely have to remove that ceiling fan. I'm not sure if that was in your plans already, but spinning blades passing through your audio signal is never a good thing!
It sounds like you know your way around tools and general construction, so you're probably aware of the difficulty, expense, and installation tradeoffs with each type of approach. To me, it sounds like you would like to gut down to the studs and then build back the way it should be with the screen on the East wall....but also realize that this approach would blow a small budget out of the water before any finishing work was started. Even if you don't go whole-hog, there is definite benefit to an absorption-only approach by installing a handful of Owens Corning 703 or 705 panels at key spots in the room. Having a drywall palace with all hard surfaces is definitely not optimal.
As for painted star ceilings, consult with Jeff at NightSkyMurals. Here is a thread on AVS: Star Ceilings... Painted or Fiber optics?
and his website: http://nightskymurals.com/
You will need to install black lights to 'charge' the paint. Jeff will travel to you and do the painting, but I am aware of some folks buying his special paint formulation and going at it from a DIY approach.
I'm also glad to have you following along in my thread. Construction recommences around September 15th, FYI.