Nice. You may have some issues with in-ceiling overheads for such a low ceiling. My ceiling is about 7ft 9in, and it was tricky getting Atmos dialed in. I have a "soundproofed" room, so I wanted as few of holes in my double drywall with GreenGlue ceiling, and that was suspended on a whisper clip & hat channel isolation system that made it nearly impossible to find the right locations without hitting a joist or hat channel to put a speaker up into the ceiling.
So I had to go with non-in-ceiling speakers. I went with on-wall M3s that the fronts were mounted using Axiom Full Metal Brackets so that I could angle them toward the listening area due to the low ceiling. The rear overheads (also on-wall M3s) were mounted on just a basic wood block that was cut to give them an angle towards the listening area more as well.
That was all in the plan, but I spent weeks tinkering before I decided to relocate them completely and start over. That is a big challenge with in-ceiling speakers unless you are good with drywall repair.
So your speaker choices are nice, but your room may be your arch enemy for the overhead speaker placement.
The good thing is that the in-ceiling M3s have an aimable tweeter which helps with better alignment for low ceiling Atmos, but still not a great situation.
Outside of the low ceiling problem, your room size is nice. In fact all of your dimensions are close to mine. Mine is 14 feet wide x 24 feet long x 7.75 tall.
