Wow! Congratulations. That is going to be spectacular! When is the party, and what should I bring
I am envious of your system, and wish you many happy years enjoying it with your loved ones.
Good questions! Your precision moved me to response.
a. "toeing in" the speakers means that the drivers are slightly pointed towards the listening position rather than parallel with the side walls. You will have to experiment with placement, relative to not only how much toe angle you want, but also the proximity of the speakers to the side walls, etc. Just play around until it sounds good to you in your room. There is no absolute right answer.
b. My experience suggests that the height of the surrounds is probably not that critical, and I wouldn't go tearing up sheetrock unless you find that you are horribly unstatisfied and are laying awake at night wondering if that strategy might help.
c. The discussions I've seen about 7.1 differentiate between the "surrounds" (what you are referring to as the "side" speakers) and the "rear" speaker(s). My understanding is NOT like yours; I had seen little if any debate about using multi-polar speakers for surround, but some people do seem to prefer having direct-radiating speakers in the rear. Again, it depends somewhat on the room. Likewise, your receiver may allow you to switch the speakers based on listening mode and source (using the direct-radiating rears for 5.1 channel audio and not using the surrounds). If I were you (and I clearly am not), I would try what you have for a bit. If you find that multi-channel audio is somehow not satisfying, I would recommend swapping the rear QS8's for a pair of M2 or M22's, but I would NOT put direct-radiating speakers on the sides.
d. Generally, people seem to advocate having the surround speakers either a bit in front of or a bit behind the listening position.
For reference, I am currently running 5.1 in a ~13x24 room with sloped ceilings from 9-17'. I find the experience very immersive and quite satisfactory. So all my conjecture about your 7.1 setup is based on reading others' experience, not my own.
Hope you enjoy your new system! Post pictures!