there are several videos and blog posts regarding 10,000 hours. put 10,000 hours into your craft - be it photography, small engine repair, professional coffee brewer - and you'd by then have the necessary skills and experience to do something for a living.
I take that with a grain of salt, and add that when you no longer feel it necessary to ask questions like this, you'd be ready to start charging. Basically, when you feel confident enough to take peoples' money for what ever you're doing.