I would think that you'd run it like any "open Mike" night, except that there isn't a mike, and people are limited to gospel. You could get a lot of help from Mudcatters defining what gospel is.. :-)

I would also expect your experience will be like anyone else's who sings in a pub or restaurant. You'll have people trying to talk louder than you can sing, which makes a sound system very desireable... even just a self-contained amplifier you can run a couple of mikes off of. I sang with my gospel quartet at a Sunday brunch in a hotel once a month for a year, and we never would have survived without a mike. I had a guitar amp with a separate channel I could run one mike off of for the lead vocal, and that plus an electric guitar made us difficult to talk over.

I would also hope that the place where you're playing would publicize that it's a gospel sing, because a lot of people aren't going to want to hear gospel, You'll certainly have a more attentive audience if they've come BECAUSE it's a gospel sing.

Best of luck to you.

Jerry