Finances. Art. Entrepreneurship. They do not go hand in hand. Even if they did, that would be three hand-holds going on and it would still be weird.
After my first year as a self-employed musician, I have learned a little about a lot. Here is my greatest lesson so far: I will never be able to control my top line. (For those of you who aren't business savy, "top line" refers to income, cash, dough, benjamins, etc...) While I can certainly take steps to market myself and my skills, there will never be any sort of guaranteed income. No steady paycheck. No amount I can count on from year to year. There will be good years. There will be bad years.
My advice to you, then, is to be born into a rich family. If that isn't possible, here's the next best thing: Control your BOTTOM LINE. If you are a musician or of another trade and are considering the step into self employment, there is no greater advice than to control your expenses. Being able to live a year on less than what most people make in half of that time has proven to give me a jump start in the early phase of my music "career". It's allowed me the freedom to go on gig runs with short notice, try new things with music, and produce low budget projects. If I had run out of money, I'd be working at Starbucks and none of these things would have happened. I would be getting free espresso, though, so I'd probably be able to play that Eddie Van Halen solo that's been taunting me....
I know you need that new Tele. I know you need that new Matchless Amp. But trust me. You need to eat for the next year. Let's not be starving artists anymore.
I hope you have learned.