I used 2 way radios in a drypack attached to the student's helmet, but they don't last very long, and you will probably pick up all kinds if chatter from fishermen. (It's quite annoying). When they work properly, it's nice, but in reality that isn't very often. I know another guy who bought the helmet with built in radio, and it went bad almost immediately. Don't spend over 100 bucks on a pair of them is my suggestion.
One of my favorite pieces of 'equipment' is a good hat to keep the sun off, and a pair of sunglasses. (I like the Dakine Indo hat with the flap that covers your neck).
Do NOT let your students wear their expensive sunglasses during the lesson. I had a guy drop his fancy Oakleys or whatever, and he let go of the bar and completely turned around away from the kite to look for them. He even stopped the rest of his lesson to continue the search.
Good luck to ya man, teaching isn't for everyone and it's tough to give up your water time. You'll know soon enough if it's something you want to continue in the future.
On that note, after almost 10 years of teaching I have nearly had enough of it- anyone wanna buy a lesson operation in Florida? www.kiteboardingtampbay.com