#1
I was practicing on the E Aeolian scale and I decided to use 4th chords(root and fourth) instead of 5th chords(root and fifth). I was wonder what types of music utilizes fourth power chords? Also, what are other variations of power chords?
#2
It's very common in metal.
As for other chords: major 6, minor 6, root 5, flat 5, major 3rd, minor 3rd... All very common, throw in the octave if you like too.
Speed is a by-product of shut the fuck up.
#3
playing 2 note chords is common in pretty much all types of music. pop punk uses it quite a bit
#4
Depending on the context, 4ths could be thought of as inversions of 5ths. So, in other words, if you have an A5 power chord, the notes are A & E. If you invert them and play E & A you have a perfect 4th interval.