I am going to re-do a bathroom in our house. My wife loves beadboard which I found 4x8 sheets at The HomeDepot which are as thick as plywood and have a lip to overlap each sheet. Should I be concerned with installing this is a bathroom because of moisture??

The knobs on our shower have wallowed off of the adjoining plastic extension piece, ruining the shower converter knob extension piece completely,and ruining all of the knobs. The faucet is some where in the 6 to 10 year old range. There are no markings on the faucet of any kind that tell which brand they are. The only thing we could see was a stamping on the underneath side of the spicket marked "QMF". Has any one ever heard of this or know what it is? If so where can I get replacement parts? The faucet seems very cheap and has almost all plastics pieces if that helps. Is therer any way of fixing this outside of tearing out the wall and replacing the whole diverter and installing a new faucet?