Based on interviews I've heard and discussions I've had with brewers, the easy part is making the beer. It's running a business that's the challenge.
Since you'd be doing it debt-free, and you have an established business with a good rep to sell the bulk of your beer, you'll be ahead of the game. My friend who started the brewery in Eau Claire has been able to do a lot of things to help grow the business that wouldn't be possible if he was up to his eyeballs in debt with the added pressure to have
at least $XX,YYY income every month just to pay for the brewhouse.
If you make good beer, that's a great start. Now you need to focus on building anticipation while you get your equipment and licensing in place.
I feel like I'm turning into a commercial for the Brewing Network, but Brew Strong has a whole bunch of episodes on going pro. Jamil Zainasheff talks about going pro, both his own experience and interviewing others. Here's a link to many of the episodes I'm thinking of:
http://thebrewingnetwork.com/shows/Brew-Strong/search/going+pro plus if you do a search for Nano or Device Brewing on the site, you should find a few episodes where they talk to a guy starting a nano out in California. His brewery name is Device Brewing.
Also, the Sunday Session has a bunch of episodes where they talk to brewers who they talk about the process.
You may want to see if you can work at a local brewery to get some experience brewing on a commercial system with a commercial timetable. I've only met the guy from Angry Minnow a couple times, but he seems like a nice guy. He might be open to giving you some experience.
One of the things I remember Jamil talking about before he started Heretic Brewing is that he recommends anyone interested in becoming a brewer take a week or a month and brew
a lot. Figure out if you can handle brewing on a schedule, get experience brewing consistently. Figure out your system so you get the same beer every time you use the same recipe.
One of the challenges brewers talk about is that getting someone to buy their first pint/six-pack/growler of your beer isn't much of a challenge. You just have to make sure it's good enough and consistent enough they keep coming back for it.
I'm super excited for you. Running a business is a challenge, but if you stay dedicated to it you can do it.