Make sure you're realistic about what you can do, but if you have a good lead with something, making the plunge into full-time writing is the only way to go.

Think about what you do from 9 to 5 each weekday. Now imagine you put that much effort into something you really believe in. It's incredible what you can accomplish when you have both the interest to do something original (which everyone has) and the time to make it happen (which few have).