Thanks! For what its worth ... your "It may not look like much now, but once things come together it will be great!" is my model to try to build mine. I am in a similar boat but I am not fortunate enough to have any dormers. The only positive (I think) about my project is that it is not yet constructed and I have the option of no end window (but that is a permanent decision that I need to think about) as of yet. I may opt for a window and put some blinds on it, seal it for light but then I would need a false wall. I was also toying with the idea of building a false wall to house the depth of the speakers I have as to not have any speakers on the floor for optomized space or it could be a vertical wall in the center for the screen and leaving it open on the sides for the speaker placement. Do you have any idea of your L + W of your screen? Diagonals never do much for me because it does not tell the actual ratio or shape. I am also having a problem deciding on the screen format. I have movies in 3 aspects and if I mount the projector from the ceiling I am not sure how to adjust the zoom when necessary. I wished we would get to a final format and stay there.
After looking at your original photos again I can see that you are in the opposite direction that I think I have to go in my HT. My building is 24x60 downstairs with a 10/12 or 12/12 pitch roof with the attic space (knee walls) and I was told that the floor in the upstairs (attic) is about 12' wide. So I have a second floor area measuring 12x60 but remember that the roof will angle in on the long sides as yours does. I am not sure as of yet what width for a screen I will actually have. Your HT seems to have a much wider truss than mine. This is why I have a hard time imagining a HT in a 12' wide room with the ceiling angling in at 45? or so. At the 8' height I am not sure if I will have 4 -6 feet of continious 8' ceiling before the angle to the knee wall.
I really like the fact that the dormer is in the perfect place for you and adds usable but hidden depth to your HT.