Since the emphasis of the RP is character choices I plan on personally working with each player to make sure they are playing a character that they are comfortable with (and one that feels organic to the world). I don't see why I'd have any objections to a tiefling character. I want to personally talk to each RPer so that I can tie personal backstories into the narrative, and I think an exotic race could really add an interesting story to the RP. 

I haven't quite decided the experience level of each character, but I was thinking that novice level might be the best route.