Speedie, welcome.
1. There's no problem with using speakers having different impedance ratings. A receiver such as the 3312 should have no problem driving the speakers which you've listed to very high listening levels at typical home listening distances.
2. It's unclear why the side surrounds "must" be in-wall, since QSs really take up little more room and add significantly to the surround effect. If so, though, the M2s or M22s would be suggested to more closely match the M80s.
3. Again here, a question would be whether instead of actual in-ceiling speakers you'd be opposed to suspending QSs or other Axioms just below the ceiling. Many of our members, including Randy, use a ceiling mount for surrounds.
4. The subs that you have(depending to some extent on exactly what the Hsu is)should be sufficient, although two Axiom EP350s would certainly be excellent. Looking at the large front speakers and possible multiple subs, it isn't immediately apparent why, in contrast, the surrounds must be concealed, even at the expense of the best surround listening experience.
5. Actual bi-amping is almost never done for home setups, because of the complication and expense involved. Two separate amplifiers(receivers have no ability to bi-amp)are required with an external electronic crossover in front of them so that each gets only the desired frequency range to amplify. The internal crossovers in the speakers are removed or at least bypassed. None of the items that you've mentioned would accomplish this.
