[[size=12]I don't think that heat will be a problem for cast iron hanging on the wall behind a wood stove, given that this stuff was designed to take far more intense heat than that. Even when you start burning in the fall and taper off in the spring, your wall and anything hanging on it will only change temperature gradually, so heat-related problems like warping will be a non-issue. I wouldn't keep pieces on top of the stove, though, even if it does look rustic.
We also burn firewood, and I do have one piece (an ERIE size 8 short kettle, I think, though it hasn't got a p/n on it) parked permanently next to the woodstove, on the stonework. The biggest problem is dust and dirt, which seem to go hand-in-hand with burning firewood. Your pieces will probably get a nice coating of it in by the stove, so you (or she) will either be dusting them off all the time, or just living with it. I wouldn't hang them below the stovepipe, either, in case any tar weeps out of one of the elbow jointures. Finally, you definitely want to secure them carefully if you're hanging them over brick or stone, for sake of both your cast iron and your stonework. I would advise you to use a bigger hook than what you think you'll need, and to screw it directly into a stud, if possible. [/size]