You have some good info already on here, but I just want to add: don't be afraid to let "non jazz" instruments join. Back when I used to judge jazz festivals, I heard so many ms bands that had tubas, bassoons, bass clarinets, etc. And some of them were pretty darn good. Also, be sure join TJEA. It's a great network of people who really care about jazz ed. I have had so many people from TJEA volunteer their time to help me out in the past. Good luck.