I don't think there is a limit, but how are you going to get everyone's mac addresses to blacklist them? It is not practical.
If the hotel staff need internet, there should be a hidden SSID for hotel staff that they can use anywhere that nobody but hotel staff has the key for. You would then remove the Virtual AP that is from the guest in the areas of the conference.
I am not sure that there is a better way to do this. Blocking by mac address when you manage all of the devices that you need to block is difficult enough. It would be impossible with devices that you do not manage..