How many users do you have on radio? Do you need separate channels for say, actor staff, maintenance, security, parking? Breaking users up into groups has it's pro's and con's. If you have a lot of people on radio, the chatter can be non-stop. Users tend to stop listening for their names due to the chatter, the maintenance staff is hearing about actor issues that they don't care about or more importantly, in the situation of an incident or emergency, that user may actually have to wait for the channel to become clear to broadcast what is going on. To many hands in the pot type of situation. But breaking them up into groups can have it's own set of problems as well. Do you ever want any of those groups to be able to talk to each other? IE, an actor zone manager has spotted a problem group, they would need to be able to tell security. Budget per radio?
As far as headsets go, generally every solid commercial brand will have solid headsets to go with them. Even if they don't, there are numerous 3rd party companies out there that manufacture headsets, many better than what you'll get from the radio manufacture (and some cost nearly as much, if not more than the radio itself). You also might want to take into consideration that not everyone will need the same headset. If you have a zone manager, security or maintenance staff that is around a chainsaw pit all night, they will need a significantly different headset than say, an operations manager or ticket manager that is in a far quieter area or office.
I'm quite knowledgeable on 2-way's, everything from consumer to light commercial through heavy industrial radio's. I'll be glad to help.