You're over the dozen and counting, so a quick word from the SouthEast BassBash collective experience ... try to have a 'quiet room' available if you can.
With a handful of people it's not really an issue, but as the numbers mount the noise levels tend to increase exponentially (oh, alright, you know what I mean!).
The room with the basses and rigs will quickly become aggressively loud and wearing on the ears, so people will need a chance to rest their ears, talk to each other normally, and have a cup of tea and a Danish pastry.
Depending on prices, if you can also have one further room with a resident drummer (plus kit, natch) and a 6-string then people wanting to try basses in a band situation will have that option.
Enjoy!