Instead of a rokinon 8mm fisheye, get a wide angle zoom like the 12-24 F4 tokina I mentioned (It's cheaper than the 11-18mm, which would be like 550, and gives you a little more range, seeing as you'll be doing more filming in the sunny day, F4 would be totally fine, it seems...)
Fisheyes are just super overused, and the rokinon won't hold it's value as well as the 12-24 if you move to a camcorder later... It's worth the extra 100$ or so almost no matter way you look at it... Use a gopro if you're going to be getting fisheye while wakeboarding... far better than chucking out hundreds on a waterproof case.
Stock lens is fine for most things, but you might also want a 35mm f1.8 for a fast prime for any low light situations you may end up in.
Have a nice day, Bluename.