The problem is not that there are not enough GMs. It is that the 'nifty tools' they use are limited, as well as the client. Logging in with a normal client and only being able to contol one character, NPC, or creatue at a time, while not being able to set up any trips, triggers, or what-not is a bad way to GM. It is -hard- to set up and control an event. Starcraft has a better scripting system, and it isn't even an RPG. GMs are supposed to be Dungeon Master types. A DM sees the entire 'board' and 'story' at once, not through a single character's eyes. That is what the rest of us are supposed to be doing.
With the proper system, I can answer the questions of "How many people?" One person to set it up, one, or even no one to run it.
Though, I guess I am not the one to ask, as I see 'events' as lasting weeks or months, not hours. I would not even think of starting one that lasted less than two weeks. Not that it matters anymore.