Several of us have used original supporting characters. Primarily Byrd Man, whose cast is original by a large majority. Though he was also telling unique stories.

I'm not a GM so I can't and won't weigh in on your first question, but I will say that keep in mind it's only a three month time skip so don't expect there to be a lot of younger characters suddenly springing up to take on sidekick roles. Things are moving at a steady pace in this game, and that's one of several reasons I think it's succeeding as well as it has been.