Honestly, you don't need a whole lot to become a professional brewer. All you really need is a banker who'll front the money for your enterprise and business plan. As long as you have the equipment, the ingredients and the patience, you can do it.
Here's the rub, though.
Any "idiot" can become a brewer with money on the line (read: not the same as a professional brewer) if they can convince a bank to cough up the money. A professional brewer, in my opinion, is someone who has experience to go with that money, as well as desire, focus and a love of hard work. That's what you need besides money to be a successful brewer. Successful is all that matters in that game because otherwise you'll be closing your doors in half a year.
For those who think you need to go to school to be a brewer. I don't believe that for a second. It might help, but having that extra debt saddling you down when you need every dime for your dream won't help a bit. Some of the best brewers out there are self-taught. The real knowledge of brewing comes from experience and a thirst for learning more about the craft. I've met guys who homebrewed for 10 years and opened shop and did fine...just to make a point.
Long story short, you need a mixture of saavy, business acumen, knowledge of brewing and a deep, deep love of brewing. Having a SWMBO who understands doesn't hurt either.