The thing about original and cover, I look at it like this. There is a huge difference between playing "a gig" and "a concert". When your gig is something like setting up in the corner at a local dining establishment, then you do copy music all night, meaning songs the people know. That is what that level of listener is expecting.

Now, when you finish your CD and you want to release it, that is a CONCERT, and you book that show at a venue more suited to people sitting in a theater style arrangement, with no doubt that what they are going to hear is your original music that is on the CD (which is also on sale in the lobby, and I'll be out there right after the show to sign the cover art if you like.)

This is where there is typically a HUGE chasm between people who play as a hobby and people who play with an eye to sell product. I spent years in the first group, which in 2 cases overlapped some into the second, and now reside solidly in the second. I honestly don't care to be schlepping gear from bar to bar or chameleon places that are family dining all day and then went to go through some magic metamorphosis and become a rock club at night. That is not a slap at all to people who opt to do so, but it isn't what I want to be when I grow up.

The kind of gig you are describing is the kind where there is no "division" between crowd and talent. That lends itself to people in the category of "everybody is a singer after their third beer" wandering/staggering up into your space, maybe knocking your laptop or iPad over and breaking it. I would make it clear to ownership that this is not open mic night and inform them that unless they agree to be responsible for any damage clearly caused by a patron going where they don't belong that I don't perform. This is my show, and it is not open to people to get drunk and decide to participate. This is why I will never play (and I mean never) in a place that does not have a stage. That stage carries an implied "do not enter" kind of aura and people are not as likely to try and join you.

One guy I know carries sections of collapsible railing that he sets up to make a demarcation point between the crowd and the "stage".

Usually the patrons don't understand that this isn't a party. It's an artist doing his job. He (or she - no sexism here) is working, and much the same as they wouldn't bother the plumber while soldering pipes or the carpenter while cutting wood on his saw, they shouldn't bother the musician either.