Wow...it takes a LOT. Not to be discouraging, but the hoops you have to go through and the cost of all the stuff you need to do to be a legal microbrewery are the reason that people don't have pubs on a "just sell my homebrew" level. You have to deal with ATF. You have to have government standard measurement tanks. You have to know the EXACT alcohol content. Depending on your state, you may also be required to serve food and run a restaurant.
Microbreweries and brewpubs have been closing down and getting swallowed up lately more than they have been opening. The big boys moved in years ago, and it is really a competitive market. It's definitely a lot more difficult in terms of licensing than, say, opening a bar, which is no walk in the park either.
Add to that you have to know how to brew professionally. Homebrewing is one thing, but are you good enough to compete with commercial brews? Can you repeat a beer exactly every time? Do you really want to? How about the cost of equipment, which is enormous? Most commercial breweries, even small ones, have professionally trained brewers running the show. The average homebrewer doesn't know a fraction of what is required to brew commercially.
If you want it to stay fun, keep it a hobby. There's nothing that will take the fun out of something like doing it for a living.
Just my $.02 I've thought about this kind of thing off and on for over a decade, and I've worked in brewpubs. It's definitely a big deal to get one off the ground.