I'll add to Doug's great advice in that many builders find that the time to actually make the frame is the smallest portion of running their business. The, often, majority of time is spent acquiring new customers, communicating with customers, doing the bookwork, designing frames (and tools), maintaining the shop, ordering and receiving parts, packing and shipping off stuff and many other mundane activities. So if you find that you can build a frame a week and your business plan calls for 50 frames a year to make your income you're going to get no sleep or not make any money as you'll fall way behind your needed production rate.
This reality of what it takes to run a profitable business is lost on many when just starting out. This is one reason why we see so many slightly used jigs for sale (given the number of new jigs sold is tiny). People start with an initial capital fund that, generally, is spent soon and the need to eat and pay for housing (let alone health care or fun) rears it's ugly head.
I remember a grand dad of US frame building say that the number of people who pay for their lives with their building is far less then the number of people who claim to be builders. So just like the retail bike business a budding builder might want to have a successful spouse to fall back on
Andy