First thing you need to do is buy and read this book.
http://www.amazon.com/E-Myth-Contractor-Contractors-Businesses-About/dp/0066214688
The book is dirt cheap, and can be read in an afternoon.
Then, if you still want to start a business, take a night course in small business.
Doesn't matter how good you are at the painting part (well, a little counts I reckon), because if you don't run the biz right, you won't make any money. If you are good enough to do this skill-wise, then make sure your financial knowledge is up to speed also.
Learning how to price work has to involve recovering overhead and expenses (which is the hardest to determine initially, and the most important and too often overlooked IMHO), determining what you actual time is worth to do the work, and providing the company with a little profit in the end. If you run it wrong, it will just become like any other job, except you go to this one for free.
Look at books like this one for more help:
http://www.markupandprofit.com/books_mark.html
Don't forget, you will need to buy liability insurance, and (depending on where you live) workers comp and a license might be required.
That might give you a head start if it didn't scare you off.
