I've sort of avoided commenting, but I agree with
@BMXTRIX that we should just try to help.
One way is that a mod would be kind to put this in the Beginner forum instead of the HTPC section. That threw me off and OP would probably get a lot more responses if this was in the right place.
As for speakers, if you can do as many in-walls as possible, do it. I did and am very happy.
I also did an all in-ceiling 5.0 in my living room and while it's fine, it's not awful either. It can actually sound shockingly good for what it is.
For you, in wall surrounds are possible, so do it.
Having three in-ceiling in front does OK, but you HAVE to have speakers that angle toward the seating position. If you don't, it will sound weird.
I wouldn't bother with Atmos since you aren't able to have speakers in the proper positions up front, you'd really just be adding extra speakers because you can. It COULD help anchor the front with the base surrounds, but that's purely a guess.
As for projector,
@BMXTRIX is correct, get a light cannon. You want something that can put a lot of light on your screen so you can actually see the picture in all its detail.
That room is pretty much as tricky as it gets, but you can get something you'll be happy with.
As others have stated, don't skimp on the sub.