Just my two cents, No I would not use pegboard and yes I would use copper with sweat fittings. Copper cause that what I know and like, kind of like film. As far as peg board, don't really like the stuff too much. Although a small panel or two located where I need to hang things on the wall would be ok. If this is your sixth darkroom I'm sure it will turn out great, hope you plan on keeping this one for a while. Lets see some picture as your project progresses.

Roger