Definitely do a business plan and aim on the conservative side with your estimations. Don't forget to plan in $$$ for repairs and unforeseen events. It seems like the only way this could be profitable is to limit your overhead as much as possible, self distribute, and don't hire anybody. What kind of beers you decide to to can be an important factor too. You definitely won't make as much per volume on draft sales as you could if you bottled. But of course, that is a lot of work. Run your plan by some business savvy friends before launching into this! Good luck Baloo!
Oh yeah, and you have to make great beer (that is the bottom line that some people forget!)
P.S. don't disclude the idea of contract or "partner" brewing if an opportunity comes your way. If your goal is to eventually get a full-sized brewery up and running, that is another possible way to get there.
