I'm so terrified of Bellatrix - even as a little girl. By the way, I'm pretty sure that Rookwood is going to be a Marked Auror soon. He's probably going to be the biggest single danger.
I wonder if Snape can be pulled from the Dark side, at least into neutrality, if we befriend him early? God knows he's brilliant, courageous, and tough. He'd be a helluvan asset if he wasn't such an embittered jerk...