My first thought seems to be what everyone else thought of, too -- extension cords! Better yet, bring surge suppressors so if an iron overwhelms the system, you won't blow out the entire library.
I would put a notice on Craigslist. You probably want to put an information phone number, not the time and location of the meeting, cause you want a good idea of how many people are going to show. Otherwise, you may get an unknowable number of people.
Good luck with your new group!!