You can have multiple characters so long as they're not part of the same faction and don't give you an unfair advantage.

That is to say, you can't make an AST character who you then use to give information and/or other things to a character you made who works for Ratatoskr. Not that I think anyone would actually do this, but yeah, that's the rule.

I'd prefer that people not have more than two characters though - otherwise things can get messy.