I agree, check with the library first about food and then check to see how many quilters you can accommodate in that room.
Perhaps having a key person to call who can then screen so that you don't have more that what you have room for. Also, this key person, or someone else so designated, could handle the e-mail notices with such things as what to bring. This list would include such items as surge protectors, extention cords, seat cushions, quilting supplies, and a basic understanding of how their machine works.
I would limit the number of irons in use as they can really drain the electrical system quickly and too many are just plain a fire hazzard. Therefore I would ask for only 2 ironing boards, maybe 3, with irons for those boards only. Small irons can also cause problems.
If you can have 2 cutting stations, that would be nice. If not, then please let the quilters know the limitations before they come.
Depending on how the tables are laid out will mean how many quilters. A few quilters may prefer to bring their own tables, esp if you are using 6 ft long tables. Therefore those who are going to bring their own tables should notify the person in charge.