Mulciber,
Great question. You have brought up an interesting and perplexing aspect of our shared pursuit. When does a pursuit, hobby or interest become a viable employment alternative. As you can tell from the responders it is not a question easily answered and the results are divided between ones passion and the reality of making a living.
From a personal perspective, I have always had a full time other profession (day job)to supply the needs of everyday living; insurance, retirement planning etc. . The day job also supplied me with the wherewithall and the valuable time off in order to pursue the finer aspects of metal work. Schooling is not that easy to come by in this profession. As an apprentice you learn the trade from the smith under which you serve but you do not make much in the process. The period between wanting to be a professional smith and actually getting there can be lengthy and expensive. Training and travel notwithstanding, the real cost of setting up even a small production shop is formidable.
To a certain extent most shops are production facilities and the rules of manufacture are as applicable in Detroit as they are in ones own back yard. R&D costs are supported by the sale of product. The greater the cost of the former the more of the later you must produce in order to break even. As a business venture, it does funnel down to money going out and money coming in. Commisions are great but they can be few and far between. Word of mouth is your best advertisement and QC is or should be your guide. A sound market analysis is in order if you plan on investing your time and cash in this venture. Know and understnad your market, what to make and how to sell it.
I know several professional full time smiths. One very skilled individual teaches to offset costs and another confided to me that it would not be possible if his wife did not have a conventional job with benifits. You can see that the competing forces are love of the pursuit balanced against survival.
All the best and good luck my friend.
Peter