Balsa wood is a bad choice: It's soft fuzzy and not very strong. It *is* very light, which is why it is used for model airplanes. I'll leave it to the real lute builders to suggest something appropriate, but if you want something that is available in a good hobby shop, use basswood. It is stronger, smoother, still workable with an X-acto knife and available down to 1/32" thick. It is the #1 wood for model trains. :-)
..Bob To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html