The screen could be hung via a French cleat, or hinged to swing up. I'd be thinking around the 100" mark for the scren
Screen size could be limited by the riser height. The second row needs to be able to see the bottom of the screen (over front row
seated heads). I wouldn't assume anything regarding riser height. Start the design with seating and you can plant eyes and ears.
Plywood floor is fine. Are you after a sound proofed room, or simply want a low noise floor in the theater?
The door in the side wall would work, but watch the door swing carefully.
Speakers behind a woven AT screen should be 6" off the backside of the screen fabric, to avoid timbre shifting. Skip reclining seats,
and maybe consider a baffle wall front wall to keep the front depth as shallow as possible. It would be a tight build so careful placement
of inches would be necessary.