Well enough applications, leaders choose who they want as staff by the information provided on the applications.
Amount of GM's, yes, should be about 1 for every 50 players and also depending on time zones. Same goes with Forum Mods, time zone is crucial for how many we need of that. As for Devs, it's great to have as many as possible. The more Developers, the better because that means more progress and more items, maps, coding, etc.