Welcome:
1) I don't think there is ever too much!
2) As mentioned, I would wait until hearing how your setup will sound.
3) Considering that your couch is on the back wall and the side QS8s will be aligned with your ears, that places them fairly close to the back wall. If you place them a few inches further back towards the back wall, they will create some kind of phantom rear speakers. The QS8s are really good, I have my couch against the wall and have no walls on the side so I have them at the back and they work very well. Since your sides are so closed to the back wall, I am not sure that you will gain much from adding the rears. So I would start with 5.1, see how it sounds and if you're not happy give a try to 7.1 or 7.2.
4) The sides should be aligned with your ears or a few inches towards the back.
