In a winebar? I should think you would have to control the venue first. If you had an official 'club' type of scene, where people paid a pittance to get in, then you could ask them to be quiet if they started to get noisy, but otherwise I suspect that you would be simply providing cheap background music for the owner.
There are plenty of performers who could carry off a spot in those conditions, but they are seasoned and proficient, and have a good reportoire. It would work, but there might be bumps in the road, especially with new performers.

Go for it. It could be a great scene.