You're going to want to have at least some basic understanding of music theory and composition. Especially if you want to break out and not just play root notes all night.
Listening to others play and such is an OK way to learn some covers. I wouldn't give it much merit beyond that though myself.
If I were in your shoes, I would find a teacher. They don't necessarily have to be a metal head to help you expand your playing and ability in metal either.
I don't know what all you listen to, buy expand yourself outside of just listening to metal too. You can pick up a lot of things from basically every genre and use it in your own style and music. Just because that's a slap riff doesn't mean you can't use it in your break down. Just because there's some chords being played on bass doesn't mean you can use it as an interlude or interesting fill.
Like I said in your other thread... Seattle right now is rough. Though, looking on craigslist here you're going to see a lot of bands looking for a bassist. There's a lot of generic crap out there that I would personally not play with, but it might be your thing.
