I love Totoro! (You may already know that from my user name, avatar, and signature...)
I also love Spirited Away and actually wrote an undergrad paper about it for a Japanese culture course (it had to be about a movie that included elements of Japanese folklore).
I vote fly and mouse! And coal dust guys! Maybe Chihiro, but I think focusing on the creatures of the film would be really cute and a little easier. Plllllease post a picture of whatever you do.
Edit: OMG, have you already seen this one? LOVE.