You could use the b/r shop price guidelines to actually set up the bar itself. Rather than create a new active skill, Id just use the knowledge like an active, since there is little actually active in brewing your own brew, at least at the basic state. Granted, there is something of an artform in selecting your own hops, bitters, aeromatics and grain type, but a dissertation on my success and failure as a home brewista is probably not where this ought to be going.
Brewing in and of itself is just a matter of waiting after you combine/cook the relative ingredients. A brewery/pub could be an excellent cover for a runner bar, if you wanted that sort of thing for your PCs. If they have a kitchen, a walk in freezer makes a convienent interrogation room, and hidden rooms can always be built in for going to ground... And I imagine using awakened plants as hops could produce some *interesting* brews.
If you want some guidelines from my own brewing experience, it costs me about $30 (give or take) to produce 5 gallons of beer, and takes about 3 weeks from start to finish. The cost is about the same for producing honey wine (my favorite), but takes about a month for it to be drinkable, three for aging it nicely. Maybe a skill roll every month, the more successes the better the brew?
You could probably even count a bar as a secondary lifestyle choice for the PCs, whatever choice they make determine the quality of shop they end up getting into. For quick and dirty purpouses, 100k a month probably sets up a luxury quality bar/cafe/whatever as well as a luxury style house.
If your PCs have enough rep in the shadows for jobs to come to them, having their own personal hangout could be a great (and friendly, well armed and well bugged) place to do buisness for the team.
A few thoughts at any rate.
As yet another aside, homeade strawberry wine gets you laid.