If you were to use a picture moulding at the top of your walls you can suspend your pictures with clear monofiliment line and a clip to grab the moulding. It's a clean fix ofr a wall that will see alot of use.

Metal stud and sheetrock is fine as long as you tie the wall into the slab above to keep it stable. If you are laminating a brick wall, use metal Chicago Bar anchored into the brick with a Hilti gun and pins that will penatrate the wall by 1" or if you are a glutten for punishment, drill a 3/16th hole and use fiber plugs n screws in the mortar joints.