1) yes, any receiver can drive a combination of 4, 6, or 8ohm nominal ohm rated speakers, especially Denon. For those room sizes, you probably don't need an extra amp, the Denon is fine.
2) to bad you can't Q's why? A matching finish to the fronts would look killer. Bookshelfs can't envelope you in surround effects like the Q's. But whatever your reason, any of those inwall versions will be fine.
3) For surrounds, side or rear, I am not a fan of ceiling speakers, the defeat the whole purpose of why you have surrounds.
4) If your willing to have a sub in the room for asthetics and matching finish, why not surrounds? Anyway, subs are not as particular for matching sound, but a lot depends on your budget, the 350 on up are good choices.
5) I would not waste your time on biamping or biwiring.
