Just a quick drive-by note here, but if you plan to implement Atmos, you will want whatever speakers that are doing side (and rear if installed) surround duty to be just above head level. You want them to be able to shoot sound, unobstructed, over anyone's head that is sitting next to you, but not higher on the wall so that you have as much distance of separation between the surrounds and the overheads.
If you never plan to go to an Atmos setup, then as mentioned, about 1-2 feet above is a good general guideline.
Then again, if you do go Atmos, then the QS10s are too dispersed for an "ideal" setup.
As for your front heights, I have on-wall M3s that I've mounted to my ceiling for Atmos. I use Axiom's Full Metal Bracket for each, and it gives my a lot of angle options.
