...the wonders of metal Rhythm Guitar.

Where should I start? What exercises, techniques, songs? Any advice?

Fast alternate picking, down-strumming, single note lines, power chords, arpeggios (for the mellower parts)

There is a series of books on metal rhythm guitar from Troy Stetina. It has two parts and a book that focuses on thrash rhythms. They seem legit to me.

Here are some good bands to start learn songs from:
Black Sabbath
Iron Maiden
Quote by beadhangingOne
Are you talking about those weird sphincter-spasms where it feels like there's a ghost dick in your ass for a little while and then it just disappears?
Stetina has good books on lead work too. The first thing I'd suggest is playing your bass riffs on the guitar. That will help you get accustomed to the scale/size and will be a lot of root notes for fleshing out chords.