I think Totoro's belly needs a bit of quilting. If you use white thread and just quilt little swirls, squiggles, or a simple meander, I think that would look fine and not intrusive or distracting.
I'm intrigued by the soot sprites. I might have to check out that movie, my youngest is 12 so I don't really get to watch those kinds of movies anymore. I LOVED The Iron Giant, I think that was my favorite.