[@PaulHaynek]: At least no gag characters.

As for the multiversal stuff, that relates strongly to what kind of premise we go with. The way I see it premises for this kind of thing tend to work out in a few different ways:

The "help" type: Where someone summons people from other worlds to help them, possibly sending them to different universes to accomplish something or fight an enemy.

The "taskforce" type: The characters, or at least roughly half, are all part of a multiversal organization and work to accomplish things for them, such as protecting worlds or hunting down threats.

The "game" type: A powerful being summons people from other worlds to compete in some kind of game, that possibly involves multiversal travel.