You're right about the potential for challenge.
Let me ask this... how long are you anticipating being in that space? Talking 1-2 years, longer? Just asking to gauge your level of commitment to spending a lot of dedicated money there.
That said... it looks like an upstairs space? What's below you? Neighbors you need to be sensitive about?
What are actual room dimensions?
And are you really set on the installation angle? Not a bad thing if you are, but consider maybe just having the ceiling speakers and wiring installed if it fits your budget. I'd rather buy nicer speakers, myself! Take good care of them and they will last you a very long time.
So maybe consider doing your standard 5.x now, and save the Atmos installation for later?
So, for the first one... as I understand Atmos... I don't think you're going to have huge success building the most effective .4 atmos set up, just because of the spacing near your LP. Best usage for .4 would be Top Front and Top Rear. That latter is right out. So maybe you could do Front Height and Top Front... that could work. Check out this for better understanding of your standard
Dolby Atmos layouts.
Center Speaker, above TV is fine, angled toward you. you can buy wall mount gear and DIY as long as you are smart about it: find studs and use lag bolts and good mounting hardware. Or same with the TV. You can find Sloped ceiling adapters and VESA mounts that use Aluminum poles with NPT.
Towers: I'm going to leave this open for a moment... but look around online and get an idea of what else is on the market first... Hell, even a trip to Best Buy/Magnolia just to hear some gear is a good start!
What I will add, though, is that you want your front three to match for cohesive sound.
Surround placement: I would almost recommend getting the "Bipole" style speakers for your space... as things are tight, this will allow sound to not beam straight at your LP. That said, you can get regular "Monopole" speakers, too, without concern. I just have a feeling that the dispersion some of those Bipoles will offer is going to be welcome. And I would recommend putting them on stands rather than in-wall... if possibe. Off to each side, a little higher than your ears and at 90-110degrees (little behind you (refer back to that Dolby Diagram)).
AVR: look at any of last-years models for the most bang for the buck. Marantz SR5012 or 6012, or the corresponding Denon models... you basically need 9-channel processing and amplification for what you want to do. Beyond that, just make certain its compatible with whatever video you might want: Dolby Vision, HDR, and the latest HDMI protocols.
Subs. Definitely a smallish room. Subs work with room volume, whereas speaker loudness is "direct distance from." If you can figure your room volume, you can shop more smartly, but I'm going to guess you don't need a massive sub. You may very well want to consider two, though, for the ability to help even out the bass.
My instinct is that
SVS might be good for you. Great prices, good value, excellent customer service. Prime towers, Prime Center and Prime Satellites for under $1550 shipped. Add a sub or two and save a little more. Add 2 PB2000, and you're at just over 3K. Plenty of money for your receiver and extra equipment. ***I AM NOT trying to sell you on this, just putting an idea out there to give you counterpoint to what you were looking at.
Share the quote when you get it. And give us the room size! We will gladly help you sort through things!
What would they charge to install your room?