320 pax.....assuming the bagroom plays some AKE Tetris, could be done with 10 or 11.
I believe the crew rest that most airlines use takes the space of 2 LD3.
it's installed in the rear hold because that's where the access door is. I'm sure it could theoretically be moved, but the access is important. Can't just have the cabin crew pulling up the floorboards in the middle of the aisle to go down there.