Chris, welcome. 1.) The question of 7.1 vs 5.1 doesn't depend only on room size but rather whether there's enough room behind the listening position for a back surround effect to develop. If there's at least 4', that should be adequate.
2.) The QSs are especially effective on movie effects because of their very wide dispersion and most users like them more than regular bookshelves for that. The placement is about the same but is a little more forgiving because of, again, the wide dispersion.
3.) The Pioneer is a fine unit, but you should consider spending less on a receiver and more on your speakers, since several fine receivers are available for around $400 or less, such as the Onkyo 604 or Yamaha 659.
The Axioms you've listed would be very good, but I'll suggest that you also consider using a vertical M22 or possibly M2 for the center. You haven't mentioned a sub, but should leave room in your budget(possibly by getting a less expensive receiver)for that.
