I can't offer any advise on your receiver question(s), as my HT setup is about 10 years old (pre-atmos) and I really haven't kept up on the latest advancements, since I haven't been in the market for a new one.
However, I have a PJ with an AT screen. I don't know if you're on a budget, but I saved a
lot of money by going DIY. I bought my screen material from here:
Seymour AV | Center Stage screens. I'm very pleased with how it turned out.
Our foundations are of similar dimensions, although mine is a bit shorter, at 44'. The limitation I faced is that the load-bearing wall runs down the middle, so the room is only about 10'6" wide. Therefore, I was a bit restricted on screen size and went with 104". The room is long, though, at 27', so instead of in-walls, my fronts are conventional box speakers, all hidden behind a false wall covered with black speaker cloth.
I also have a laundry room beside the HT room. If you are bothered by external sounds intruding on your listening, you may want to consider some acoustic isolation measures, such as acoustic insulation in the dividing wall, acoustic wallboard and/or staggered studs. I find that I tend to "tune out" any external sounds, so I didn't bother with it. Just a consideration, that's all.