I can feel an essay coming on. I'm still new to photography. I find it quite like surfing. The more you do it the better you get, especially if you review your shots. The less you do it, the easier it is for forget the little things that can help improve your results.
For me the photographer takes the photo, the camera only captures it. So don't get too caught up in the camera. However, there are certain requirements for a good surf camera. I don't know all of them, but maybe someone more experienced can offer more advice.
Things like you say are: fps, but also how many shots can it take at that fps (it may be able to take 10fps but if it can only take 2secs and then buffers for 4secs you'll probably miss the best of the wave), then how quick does it save them before you can take more shots. A good memory card helps this apparently. I prefer to wait for the moment then try and capture the whole wave sequence (my camera is sh*t), but if your mate want to improve then the whole wave is the best. If you are going for the one shutter release shot then it helps to have some surf experience. But after a while of just watching you will know how your mate (and others) surf so know when the right moment is getting close).
Re: Auto-focus. Again, I'm no expert. And I think there are threads coving this waaay back when. Maybe check posts by Ricky ? The thing for me with auto-focus is that the surfer is moving, not always at the same focal length away. So you need to set the camera on continuous focus. But this refocuses for every shot (i think) so you may end up with the subject out of focus. Ie. You may end up focusing on the horizon, or if playing with DOF then you may have the wrong part of the picture in focus. I'm not sure the best way round this as I don't play with my camera too much. Maybe something to do with focal point selection? Just something to think about.
I'd personally go with the 70-300. It will give you a better range of shots you can try for. I've only got a 35-70 and it's only really good for line up shots as I can't get close enough to the action. With the 70-300 you can get close in on the action and also use DOF to compose the shot better. Just my opinion though. A tripod would be needed though as shooting in low light often means the distance shots will be hard to get sharp. Move around to vary your results or you'll get the same bland 'from the beach' shot. Get some elevation, go down the beach. Sorry if this is patronising. A while i'm being so... also keep in your head things like, subject matter, framing, foreground/background, rule of 3rds and all the other things that every photography site will tell you.
The best thing you can do is scan through the surf magazines and see which pictures you like and why you like them.
I've got personal preferences that I like when looking at surfing pictures. But don't really want to go into them as what one person like another doesn't, plus I'd just be talking more sh*t. The Surfer's Path and Surfer's Journal do photography profiles and are good to read as the photogs talk about their shots, how they got them, what they like about them etc. All food for thought.
If you not too shy, post up some of your favourite pictures. Yours/others/surf/not surf. Sure people on here would offer there opinion. Or there is a thread for 'pics on MSW' that has some good shots to review.
A large sensor should give you better shots in low light (can someone confirm this?) so may be better if you're not always taking pics on a sunny beach.
A polarising filter may also be handy if your shooting into glare on the sea.
Most importantly. Don't leave your camera on 'crappy tiny pictures' setting after using it to list ebay stuff and then forget to change it back for your epic surf session when you get your best photo yet only to discover the file is 0.5mgb and thumbnail size.
Showing it's good to be creative and not alway follow the 'rules' rigidly.