Is there a limit to how many characters you can have in play at a given time?

Well… there is some (quite high) upper bound, given the limit of 3 of any given card in a deck and the fact that the number of published cards is finite (not to mention restricted cards and unique cards).

Other than that?

Dark Initiate is correct, but just to make sure the point is clear, No, there is no game limit to the number of characters in play.

Alright that's good, wanted to make sure few of my games have had about 6 characters in play before. Seemed odd because they were stomping all over the stories but I guess the other deck just got unlucky in countering mine.