There's no reason you can't have multiple ones! Although, if you plan to adventure in and around Daunton you might want to make it so that your sister actually travelled over into this area instead of staying in the Imperium. That way, a DM could say, arrange to have their adventure perhaps given to you with her as the client. Hah! Imagine that, you could end up adventuring for your sister, with neither realizing their blood-related but still distinctly different races.
I usually DM too but I think that only spurs creativity when it comes to making PCs. For many of my games I make these short stories for NPCs that only end up dying. I hate the idea of a DMPC so what I do is set up interesting characters as enemies. Everytime the group gets a magic item it has a history and a person attached to it. For example, I'm soloing a game for a friend and he's going to be getting a +1 Distance Longbow. The longbow is in the possession of this young boy mercenary in the next fight his party is in. The mercenary is an enemy but I wrote up this short background for him and plan to drop little bits here and there. Such as the bow having a carving of a minotaur skull on it [the boy's family was killed by minotaur savages and he hunts them as a side profession]. Ah..I digress.
By the way, you can start RPing in the tavern before your PC is approved. Come join us! A couple of us are already RPing in the Hanging Man.