There are a lot of both business, and in particular, getting started threads here already. Help yourself.

Making stuff is one thing, selling it another, and making your sales add up to a profitable enterprise a third. People can be successful to different degrees in the various boxes. Much of what makes a craft business successful has nothing whatever to do with building. And it goes without saying that those other bits are far more rewarded in other areas, which would tend to suggest that bike making would make a better hobby than a business, but then you run into the fact one can only own so many bikes, and the cost of making the first one would pay for a lifetime of custom frames, at least the way I went about it. So my feeling is that the main requirement to make frames is desire that passes by common sense. That won't take no for an answer thing.