1. Yes, I use 3. Generally not at the same time though. Only if I'm lucky do I get to use all three(generally if i want to use a multi patch on the xpander).
2. 6/7-10. Depends on your approach. Once you understand the OS it becomes stupid easy to use. The way it operates is a slightly simple/easier to use machinedrum, with the dual functions per knob/button.
3. Absolutely! You could even dual control two pieces with one orb. One via midi, the toehr via cv. It's not to useful(because it'll be on the same sequence(r)), but it's worth mentioning.
I find them to be extremely useful. It wouldnt be the case if I had two sets of hands, but hey whatever.
Time for updates: pro-1 x2, Xpander, 808, mopho, SEM, PolyE, Voyager, Fr-Revo x2, XS, DRM MK3, KP3x2, mf104z x2, mf105m, mf103, space/time-factor, t3, nord g1..(plus other effects/sequencers/samplers and other shit).