We cannot get over what ballon artists like Brian Asman of Balloons Equal Fun and Asi Cohen (who owns a balloon company based in Israel!) can do with a little plastic and air. We love the caricatures Brian does for party guests and the dresses Asi makes (some posted here). Maybe they will inspire you for your Mitzvah planning!
When it comes to figuring out if your event will be balloon-friendly or not, Brian offers this advice: Please keep balloon sculptures away from sunlight, heat, sharp objects and mean people. Length of an event is usually not an issue. Some installments are meant to last for days or even weeks. In this case, a small team of artists needs to be on hand to check the sculpture every morning and make any necessary repairs.