I have recently been working on Victor Wooten's version of amazing grace. I want to do some of my own improv as an intro and some throughout the song, but I have no idea what scales/modes/chords I should use. Anyone have any advice?

I'm not sure what key he plays it in with those harmonics but I don't recall him changing anything drastically. If you have a realbook I think there is an Amazing Grace chart in it. If not, try searching for a pdf of it. It should be easy to find on p2p or web search engines.

G mixolydian. If you're using natural harmonics like Vic, they'll limit you.