I'm looking to do stuff like Dub FX and Woodnote (if you haven't heard of them: http://www.youtube.com/watch?v=WhBoR_tgXCI&feature=channel)
The only thing is that I'd integrate my guitar playing into it.

So I need a loop station and a multi effects unit.

I was thinking of getting a Digitech Jamman ( I like how you can save loops and connect it to the computer). I was just wondering if there's any reason why I should go with another loop station? (in the same-ish price range)

As for the Multi-FX, I'm completely clueless.
All I know is that I'd like something that'll give me good tones (not just half decent) and not too digital if it's possible. I'd like to use it with a mic (for the voice) as well as with the electric guitar.
Is it possible to get something like this under 600$? Best bang-for-the buck, I guess.

Finally, would it hurt my Vox AC15 if I sang/beatboxed into it? Or should I use some kind of solid-state amp?

Forgive my lack of knowledge..