If you have never built a frame, I really think you are getting ahead of yourself. However, to address the most important question, framebuilding is either a part time job, subsistence living or something you do while your S.O. keeps the household afloat. Unless you are a natural, you aren't going to get from nowhere to thriving in a reasonable amount of time. The insurance question has been beaten to death, but I think you owe it to your customers to carry liability insurance. And you owe it to yourself to figure out how to carry that insurance for the lifetime of those frames. There would be a lot more part-timers if it weren't for insurance.

The bottom line is that every one man business comes with a full-time position in sales. Is that how you want to support yourself? Furthermore, making a frame in a reasonable amount of time is something that takes practice. So you're wasting time coming and going.