Probably the first question to 'prime the pump' would be: How much money can you invest in a 'micro system'? In any bussiness venture you have to 'run the numbers'.
1. How many of the 'product brews' do you suppose you could sell a day, week?
2. How much more could you charge for your 'product brews'?
3. How many hours a day, week could you devote to brewing your own 'product brews'.
Spread-sheet these questions and you will extrapolate what size system capacity for starters. Extract brewing would be exponentially more expensive the larger the system capacity.
My experience in the 'bar-bizz' is that patrons won't care what quality they're drinking after a couple of 'units' (drinks-beer, wine, mixed, straight). Unless you have a sufficient and dedicated clientele of connoisseur beer aficionados, your venture might not be worth the time.
However, there might be mitigating factors that might redeem this idea; new and changing 'product brews' would draw patrons from other local establishments (when you 'seat' a patron, they usually will stay).
Some other notes: Assuming you keg 15 gals in 3-5gal soda kegs. That's 40 pint glasses until you have to go back and change kegs. Might work like some 'happy-hour' promo. 4 buck pints times 40= $160 per keg. Larger kegs....................
Then don't forget creating and maintaining a 'backlog' of conditioning brew. You would have to set up an area of rotating kegs at the ready point depending on how much 'product brew' you would need to keep interest.
Unless you want to keep your labor of love and periodically introduce a couple kegs, here and there, it might not be worth the time. And, in your state, is there a standard and license you must have to have a brewery on premises?