One barrel a month!? What is that a ten gallon system brewed once a weekend? That volume is so low you won't ever be able to keep one client happy.
There is plenty of information out there. Get on Google, write a business plan, and actually think this through. I don't think you grasp the amount of work involved with this only to be losing money the whole time because you are so small a "brewery"
Here's a really interesting thread for anyone interested in "going pro."
In short, yes, it is possible to do so at the 1bbl size, though you won't be making much money (and none in the first 6 months or so while you pursue all the licensing and permitting that's required) and you'll sure as hell need more fermenters so that your capacity will be more than 1bbl per month. Be prepared to invest a bunch of money and time up front, then lots of time as you continue to run your brewery.
Or, you could do like the rest of us do, and keep it a hobby and keep it fun.
Keep in mind you can distribute to your friends or brew batches for them by having them buy your ingredients for you. Other than that, you can't legally sell or distribute to them or retailers without proper licenses to be a brewery.
From what it sounds like to me is that your friend enjoys your beer a lot, but have you submitted it to any homebrew competitions to see what critical judges think of your beer? Have you won any competitions or entered into any pro-am contests? That validation from judges and winning competitions will make your product more marketable, but otherwise you are wanting to embark on a long windy road that isn't for the feint of heart based off of the tastes of one friend.
For distribution you would be killing yourself brewing every day to keep up with even a small clientele, if you were opening a tasting room you could do it in your off hours if you were only open an hour a day and had mediocre beer and some good friends.
This has been covered many times but a 1/2bbl system with a tasting room is still a crapload of work but doable.