heh....

A) Poser 6 supports true reflections I believe, but since you want a differant face staring back, probably your best bet would be to render the scene as it will appear in the imge. Then make a seperate render of the scene, looking OUT from the mirror, possibly with the reflected demon/nasty replacing the character. If you save the pose from the character, then apply it to the demon, it'll be correctly posed. And then you'll need to composite them in your image editor.

B) dunno....but the first place i would try is samildanach who does some wonderfully macabre texture sets.

C) again, no idea....personally i'd just make one

 "That which doesn't kill you is probably re-loading"