If you plan on having 2 fins for your IS 101, you can try the Venom 34 first then decide if the 34 will be your light wind fin or high wind fin. After knowing so, you can either get a 36 or a 32 as your second fin. The C3 fins cost a lot less than the debs. It may still be with in your budget to order all 3 at the same time.
These fins are like 2 fins in 1. A lot of grip at low speed and slippery at high speed. They are also raked back quite a bit for better control.
I like using smaller fins. I wouldn't go smaller than a venom 36 for my IS101/ 7.0 set up.