Just get something a little less powerful until you get a handle on riding it. You can really fuck yourself up riding something too powerful, like a 2-stroke bike. That's like putting a newbie on a crotch rocket! They'll fuck themselves up.

Just get a 4-stroke. It still has balls, just not as much kick. A 250cc or even a 150cc. Depends on your height and weight though. If you're just a little person about under 150lbs, I'd get just a 150cc. Any bigger than that, go with a 250cc. I don't recommend buying one any more powerful than that until you get a handle on it.

If a buddy has a bike, practice with theirs beofre you go and spend a shwack load of cash and fuck yourself up.