First, take a course to learn to ride... That was my first step. Then I rode a relative's 500 for a summer. This year, I decided to buy my own bike, an 800. But to start with, power/size isn't really an issue. It's learing to ride! I'd say a 600 would be okay. But if you found a 500 to be more affordable, I wouldn't hesitate to pick it up. You won't lose a ton of money if you buy it used and take care of it for a year or two. And you also won't be out lots of money in case you do make a mistake and dump it.