If you're riding boat and your water is fairly rough get a board that has a more locked in feel. Something with channels and fins.
Since you're a snowboarder some may suggest a "flex" board but I'm still of the opinion that traditional (rigid) boards are better for boat riding.
If you're going to hit up that cable park in NC from time to time then a flex board would be a better choice to do both.
As for kite boards. They are designed quite differently and while you can make some boards crossover for wakeboarding to wakestyle kiting you really should get a board that is specific to each sport. In addition to that you don't want to learn to kite using boots at first so a kiteboard with straps would be a good choice for that. Almost all strapped kite boards with the exception of some wakestyle kite boards DO NOT cross over well for wake boarding.
One final note on learning to kite. Get lessons! Buying a kite online and trying to self teach is a sure way to seriously injure yourself others or worse...........