Guild Wars 2

if someone creates a custom arena, does that mean only one match can be played in the arena at a time? or is it more like a “ruleset” that can be used to generate many instances and thus many simultaneous matches?
(i assume the former since it’s the stingier option :p)

also, is there a limit to how many people can spectate a match? or could we conceivably have some match that’s popular enough to have thousands of spectators?

I think it’s one match per server. Limit of spectators should be unlimited.