I might just work on both characters and then PM them out or post them just to get some thoughts on them.  

Those are some good suggestions on magic.  I was definitely considering some sort of shadow-based stuff for the thief.  Probably either some amount of manipulating shadows, or teleporting between them.  I think for the detective type I had some thoughts of some sort of supernatural awareness.  Not sure how best to do it, though one thought was a sort of ability to sense everything around her in a certain radius.  Analyzing weaknesses is definitely a good one.