At the bottom of the picture, is that an entryway without a door on it? To me that would be a bigger problem. I would want some form of door there to keep out the light mainly, and the sound, if possible.
I'm also assuming that the screen goes at the top of the picture. 6'10" is not big enough for a decent sized screen. I thing you would want a minimum of 9' up to 12' of screen, especially if you went 2.40 aspect ratio (which I prefer, but some don't). That back wall sure looks like a good place to place speakers and use an acoustically transparent screen.
