There's a lot to consider - welcome to the madness!
The room sounds fine. As you noted, the lower ceiling is a bit of a limitation, but if you can work out the sight-lines with a 7" riser, then that's fine. You may look into offsetting the seats left-to-right so that heads don't line up so much. Also, I'm not sure that heights will be worthwhile. Have you seen this thread
It sounds like you have decided not to do much about changing the actual construction of the room. That's okay, but let's lay out some of the reasons you might come to regret that. First, ventilation. Keeping fresh cool air in a sealed room is a serious challenge. Failing to meet that challenge can be a serious shortcoming when you want to have a few friends over, but everyone is sweating half-way through the movie - that can happen! HVAC is one of the most talked about design criteria here in some of the builds. Second, sound isolation, or soundproofing. If you can't enjoy the theater late at night because it bothers the rest of the household or the neighbors, that's a problem. Also, if you keep reaching for the remote because the sound of Fido's paws in the kitchen overhead drown out the dialog, that's a problem. And while you can improve the sound isolation characteristics of the space without tearing out the drywall, you can't really get to what most of the DIY builders here expect without removing and decoupling the wall structures. (I don't want to belabor the point, but I don't want to let you go without mentioning it. There's lots to talk about if you want to consider these things.)
Your basic plan for treatment should get you pretty close. It's tough to say up front, and it's tough for you to know in the end - unless you either hire a pro or do the legwork to measure the acoustic response of everything.
I don't have anything negative to say about your power plan. It seems fine - depending on what you do for subwoofer(s).
You'll need to consider screen and projector together with viewing distance to know what gain screen you might need. The sales guys at AVS are good at that, and only a phone call away. That said, I'm sure others can help, and the dimensions and gear you're talking about are common. I'm slightly concerned about it being too dim, but finding at AT screen with higher than unity gain might be problem for the budget - and there's very little woven that fits that description. Specifically on the projectors, consider one with lens memory. The JVCs and Panasonics have this, but I don't think Epson does (at least in this price range, maybe at all) - not sure about the Sonys. While, I agree it makes sense to set the screen for 2.35, you'll want to adjust zoom for 1.85 or 1.78, and having power for zoom/focus and memory can be a real plus there.
On the amp and receiver issue, it seems to me you're over-spending. I'm not sure, but it seems to me you can get better value with either a less costly receiver (with pre-outs, obviously) or going for a dedicated processor. And have you done the math to figure out how much power you'll need, given you listening preferences, speaker sensitivity, and seating distances?
The real processing decisions you have to make are with the 4 side surrounds you've suggested and with the subs. Forgive my laziness, but I'm going to copy what I posted in another thread
a few days ago.
If you go with one set of surround loudspeakers, which is what 99% of everyone does, you have the layout correct, IMO. Put it just behind your main listening position. Everyone else just gets what they get, in terms of sound quality.
If you want to get into using more than the standard set of surround channels, you have some reading to do. First, https://www.avsforum.com/t/1455111/when-are-multiple-side-surrounds-necessary
a thread where J_P_A asked basically the same question you did and got some good answers. A few days later another thread was posted and got some more good feedback, especially from Roger Dressler, here: https://www.avsforum.com/t/1488704/having-four-speakers-as-surround-for-two-row/30#post_23771038
. A few months later, it came up again. Finally, Nyal Mellor gave what I think is the most clear explanation of what to do to get mutliple side surround channels calibrated properly, here https://www.avsforum.com/t/1493743/processing-for-multiple-surrounds#post_23814755
You can do it however you want, but doing it "right" comes with a pricetag. smile.gif
The keys, IMO, to getting the smooth, tight bass response you're after are: several subs (4 is a good number, but 2 is better than 1), and independent processing, including delay, phase, level, and EQ. MiniDSP is a good choice. Have you considered building subs? They're dead easy with a few tools.
Can you post a layout? Have you considered access and control of your equipment?