#1
How can I improve my alternate picking?

I'm having massive problems alternate picking on the E and A strings, my pick always mutes the note and I think it sounds horrible, is there any way I can be more fluid?

And my alternate picking, I can do it with single notes, but when I'm playing more than one note simultaneously in fast succession, I just end up hitting all the strings, so I tend to stick to downstrokes, is this a problem?
#2
its not necessarily a problem, but you'll want to alternate pick in the long run, once you get in the habit of it, it's MUCH easier to play.

the only advice i can give you is to practice a lot.. it will come
My Guitars:
Gibson Les Paul Studio
Epiphone AJ
Ibanez Strat Copy

Amps:
Orange Tiny Terror Head
Old beaten up Peavey cab
Marshall MG30DFX
#3
Do you think I should go back powerchords, just strumming them slowly and building up speed?

And also do I need to change my stlye of holding the pick, I kinda hold it at a 45 degree angle facing up, is that alright or do I have to change?
#4
there are a couple of videos on Youtube that show exercises you can do, just search for "alternate picking"

wouldn't say that using all downstrokes is necessarily a problem per-say. I lot of stuff sounds better with all downstrokes, like The Ramones (pretty well most punk actually), or Master of Puppets

But if you're going to want to speed up your playing, you're going to need to practice it. A lot of stuff doesn't work with all downstrokes, mainly black metal or anything fast or tremolo picking