I too, started on a 600, but I have lots of dirtbike experience, plus I have ridden many street bikes, from cruisers to 750Rs. The difficult thing about 600s is the lack of low end power(I feel). Its difficult to addjust to the snap of power at 10K Rpms. The SV 650 would be a good starter bike for you with your size and weight. They have friendly powerbands, and you can grow into it a little more than a 500. Like Nomad said, take the course first and see how you feel. Good luck.