We are at least going to use black out curtains to cover the windows. And obviously move the attic door all the way to left. I hope I can find a deal on a JVC X500, and would your at least a 120 inch screen. Not sure what brand of screen or throw distance for the projector.
You have a lot of audio gear to buy, which is why I didn't suggest a pricier projector and screen. The JVCs are relatively long throw and not particularly bright, so a large AT screen is pretty tough. A brighter projector can get away with an inexpensive, lower-gain, spandex AT screen. Even with a 1.4 gain non-AT screen at 122" and in dynamic mode, my RS1 never really had the pop I wanted and AT screens with true gain are going to eat even more of your budget. You didn't mention your expected content, but if they include 3D movies, remember that the 3D shutter glasses essentially make a projector half as bright as in 2D mode.
If you plan to put the screen on the left hand wall with the door that is to the attic, then I don't think I'd move the door. I'd leave it dead center and mount the screen hinged on one side so it can swing out when access to the attic is needed. If you move the door to the side, you will end up with a left or right front speaker in front of it which would not be good acoustically. The center channel can be above the door if you leave it where it is. Orienting the room that way is going to allow a non-AT screen, which is good budget-wise and gain-wise, but leaving walkways on either side of seating means only 3 seats per row, and a second row blocks the entry. Having more than one row kind of dictates a larger screen, as well. The minimum distance needed between rows means that a smaller screen like the 120" is going to seem much smaller from the second row than it does from the front row. The plus side is that a 150" screen is 11' wide and nobody will be sitting off-axis, so a higher gain screen can be used without that particular off-axis dimming issue.
I wouldn't close off the dormer areas with just curtains -- they won't contain the audio.