Meeting with multiple attendents

I want to organize EVENTS. Not one-on-one meetings. An event has a number of attendents. Sometimes you want a minimum to attend to make it affordable. Also for certain locations or type of events you can only have a maximum of events. This can vary per event. Like a live class. 4-8 persons. Like a online seminar 1000 persons. etc. Also per Event: - you want an event organizer - you want to create a group of organizing team - you want to create multiple groups for the event as Facilities, Presentors, Support, etc - you want to add a mailinggroup (people who made an appointment), for instance to sent a poll after the event