I just did a character selection for my game, here is how I did:
-First I made the character selection screen, with Actors using the images of the characters, on each actor, when clicked, it would set a game attribute called "Character_chosen" to a number.
-Second, in the game itself there was a conditional that "added actor X to the scene" depending on what was the value for the "Character_chosen"
I think this is an easy way, the one I made actually saves stuff in a list for using different save slots. Hope you can get it working.