+ 1 for the idea by russ69.
I'd start with selling used gear, which would keep your initial investment much lower. Plus, your ever changing stock of reasonably priced equipment would keep the bargain hunters coming back to support the bar and/or coffee shop.
Selling anything is hard; but, selling something you believe in should make it easier. People are probably more sophisticated these days, so I might try to feature or specialize in some equipment and speakers that are both visually appealing as well as having quality sound. I'd certainly like to hang out in a place like that.