I have similar room dimensions for my projector set-up, though it's admittledy one semi closed-off part of a big basement.

If this is truly a custom job in terms of cabinetry, etc., a lot of home theaters are built with a stage in front of the screen. You could easily put the CC on a stand/cabinet there and flip it upside down to angle it upwards. I do this with my CC and find no vertical "movement" in the sound during L-R pans.

Don't worry about back surrounds in a smallish room with QS8s...they do such a fantastic job, it's not worth the expense or pain of mounting other speakers. In my room, the couch is against the back wall with QS4s overhead...we miss nothing in terms of surround effects. Front height surrounds? Try before you buy, but again, what are you worried about missing?

I would follow the suggestion of JohnK and put the L/R M22s outside the screen. It will look great. All that stuff about toe-in is more about sitting in one precise spot listening to music than movies...receiver-level volume and delay adjustments should be able to correct for deficiencies of in-wall front speakers based on where you're sitting. That being said, not likely to notice in your size of room.