I was just about to comment that Witcher style magic would be great! Hot babes casting spells and shit (and maybe a hot Geralt here or there - different strokes for different folks). Yeah, this looks pretty good!

In regards to the scale of the world and the families in it, I would go for the minimal approach. As Buddha rightfully said, lack of interactions in RPs are like instant death for them. That's the tricky part with these types of RPs, you want to get everyone together to get a lot of interaction but having everyone together reduces the scale of the RP and the potential for devious plots.

If I were you (and this is just a thought, don't take much sense from it), I'd shape the RP into like a hybrid Nation RP with focuses on armies and states but also a focus on character interactions. Timing is a key issue as well - don't get locked down on a single day. Take from that as you wish, I'll just go and look pretty in the corner!