Welcome,
First, the M80s will not disappoint. I urge you to buy them if you have the space.
1. You can use a receiver. I am in a 4,000 cubic foot room, I sit 8 feet away, and I run them with a half watt nominal to produce 85 to 90dB with a 90W/channel Denon. Denons and Harman-Kardons have no problem running M80s. Other receivers work as well. If you have a receiver, try it. What receiver do you presently have?
If you have a need for lots of power (150W+), go for separates. If you listen to late era classical, you may want to look at separates as well-recorded classical has very high dynamic range. You can use the receiver for the centre and surrounds and an amp for the two fronts.
2. The VP150 is shielded.
3. There's nothing wrong with using floor-standers for surround. Experiment with positioning. You may achieve a more realistic surround effect if you direct them away from your listening position so that you can't localize the sounds.
4. I don't believe any receiver sounds different from another. There is a debate as to whether some implement multi-speaker modes better than others. However, there is no credible evidence to suggest purchasing one over another based on sound quality. If you are planning on purchasing a receiver, look for the features you want/need and the ability to drive a 4 Ohm load. Most are not rated for 4 Ohms but will do it anyway.
5. The advantage of sealed is greater accuracy/less distortion at the expense of low end and loudness (sound pressure). Some claim that sealed subs can't approach the transparency of ported subs. I use the EP600 ported sub. What's amazing about it is that it works for music and movies. It goes deep, is very articulate, is smooth and transparent and it rattles your house when it's called to do so by the source. Put the money you save on surrounds/rears to a good sub like the 600. A sub is a must no matter what speaker you get unless you only plan to listen to flute music.
6. Like I said, I play my 80s with a half watt nominal for music. For movies I turn them up to a few watts nominal. Right now they are playing at less than an eighth of a watt so that I don't wake anyone. The music is still coming through clearly but I prefer to have them turned up.
The M22s sound thin, clear, more transparent and are less forgiving relative to the M60s. Some people like that. The 60s sound more full, laid back, more forgiving and mellow at the expense of clarity. The 80s combine the best features of the 60s and 22s but are not forgiving. If you have the space, go for 80s.
The best sound I've heard comes from placing 22s on top of 60s and running them both together as A+B. If you have music that hasn't been recorded that well, you can then switch the 22s off in favour of the more forgiving sound of the 60s.
Let us know what you decide to do.
