I don't think any of us actually drew on Gravity Falls specifically, but given that personally I'm a huge fan I wouldn't be surprised if a bit slipped in here and there.

Personally, my main inspirations for the game are fairy tales and Disney movies. The sort of standard that I generally use for determining if something can fit in the game - if it's not too dark, or too cheesy, or whatever - is "would this happen in a Disney movie?" I think we've stayed within those boundaries pretty well, heh.

As for the music, I can't speak as to the composers themselves, but the references that I gave them were mostly film or game music, ranging from Nightwish to the Golden Sun Soundtrack to other visual novel soundtracks.