#2
first of all, it should be BM7, which means "b major seventh". the chord is spelled B D# F# A# and so since it is a major chord it fits right in to the B major scale (B C# D# E F# G# A#). that's the short of it, anyway
#4
That would depend entirely on the progression.
Someones knowledge of guitar companies spelling determines what amps you can own. Really smart people can own things like Framus because they sound like they might be spelled with a "y" but they aren't.