Think about the microclimates on your walls. I live in a region where temps can vary from -20 to 110. I would never put an instrument on an exterior wall.

As others have said, consider moisture from the kitchen or bathroom.

Don't hang an instrument where the sun will shine directly upon it. Don't hang it over a heat register.

Make sure nobody will brush an instrument with a shoulder and knock it down.

If you have any wall space left once the problems are dealt with, I think it's a great idea to have instruments out in the open where they can be grabbed and played whenever the mood strikes.