#1
Yeah, so I'm learning music theory 'cause I want to make music. Thursday I learn a little something called "Chord Progressions" that mostly every song has and have heard how it works. I sort of understand it and I'm getting closer to compose a song I have stuck on my mind, but since I'm a metal freak, I've been puzzled at how power chords are used in songs. Are they used as major chords because of their 1st and 5th notes or are they something else altogether?
#2
Powerchords are ambiguous. They lack a third, which means their tonality is determined by context. They can replace any chord in a progression except for the vii in a major progression and the ii in a minor progression, because those chords have a diminished fifth. The theory sticky explains basic chord contruction/function and progressions.
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.
#3
Powerchords are the root, perfect fifth and octave.

Due to lack of the third you can not have a diminished powerchord because it would have to have a flattened third and flattened fifth to work. Even if you flatten the fifth it would not be diminished.
#5
no kidding. honestly hardly anyone is gonna notice you sharpened the diminished fifth in the seventh.

what i try to do is for the seventh, use a Aaug5. Ive notice many bands use this "power chord"
like switch from C5 to Baug5. or even B(b5) sounds interesting.

taking a normal power chord then changing the tone by either dropping the root a half step or raising the fifth a half step. Lots of emo bands do it.
If you dont find theory interesting, then DONT study it. IF your TRULY serious about playing guitar(enjoying), then EVENTUALLY you WILL WANT to study it.
#6
Yeah, it's also true that if you're playing mostly powerchords nobody will be paying enough attention to you to make it worthwhile looking at theory.

I'm yet to see a 'how do I play this...' or 'how do I get that awesome style' concerning Greenday in here as an example.