Chip,
These are interesting questions and I'm sure you'll receive many different answers. My wife and I formed our business (Bear Dance Joinery) when she had almost three years of TF experience and I had almost two. That time was spent working at a couple of large shops where we participated in cutting several frames. After we formed our company, most of our early jobs were itinerant positions working for other timberframers. Over the years, this has continued to represent a large part of our business, though we do cut our own frames here in Virginia or at clients' sites. I think that when thinking about starting your own business, your experience becomes less important than your motivation. I know some framers that had very little experience before striking out on their own, but they had serious motivation, a willingness to learn, and even a willingness to work for less money while they learned. Starting and running your own company is more than a full time job. If this is a path you are thinking about exploring, make sure that you have a strong sense of dedication and focus.
Good luck,
Bob