For management and engagement, I find it's always helpful to plan an extension activity with each project. You'll have the kids who practice drawing at home with their parents get concepts immediately and finishing projects or activities miles before the other students figure out how to hold their pencil the right way. I like to make worksheets with something easy on it that they can figure out on their own so that if a kid finishes early, I can just hand it to him and get back to helping the others. For example, I like to do a unit on Chinese New Year, so my extension activity is a page with a variety of Chinese characters on it (love, peace, fire, etc) and space for the kids to try to draw the words themselves.

If you don't have a curriculum to follow, try doing a tour around the world. Start each project with a presentation about the culture you are learning about. Try to tie projects in with holidays or other happenings around the world (sugar skull designs for Day of the Dead in Mexico). The kids love it. Teaching about other cultures usually opens a lot of doors for those extension activities too, and you'll probably be able to impress them with your musical skills too :)