Since you mentioned the JP...when i was 70kg and supping lots i was using the jp 9'3 surf. It will atake a session or 2 to get dialed in but dont stress. It also SUP sails very nicely. I also had the Tabou 9'2 but with its extra 30L of volume you might struggle to turn it. However i did find it to be the best SUP wave sailing board ive tried yet. I also tried the 8'10 JP but never got a good chance to give it a fair test. I only sup sailed it once if i recall correctly, it was too windy while i was demoing it. If you can get a demo give them a go!! But try at least 2 boards before you make your call. Supsail and SUP if you can, coz some boards are better than others in each disipline. As an option for teaching windsurfing, in general SUPs arent so good unless they are super wide with a centreboard. you cant have your cake and eat it too unfortunately. sorry.