I would not use peg board for the walls. Not sure what they are like now, but in my darkroom, all but one wall was just framework with insulation over it. I just nailed in a bunch of garbage bags over the framework and the plan is to put ply-wood over that. If you want to use peg board, i'd put it over plywood or sheetrock. just make sure you make a frame around the edges, using 1x1 or something, so that it can stick out from the wall a bit. Personally though, i'd rather have some nice shelves on the walls than peg board. I don't find that a lot of darkroom stuff really fits on peg board hooks real well.
Instead of pegboard, I would use slatwall. You use it just like any other wall product, with the convenience of brackets that allow shelves and hangers anywhere.
pegs eventually fall out of pegboard. I really hate the stuff.
I have a lot of shelves prelaminated and put up with 90 deg brackets. There must be 30 feet or more in the original 8x12 room which is now the wet room. Enlargers moved to separate adjoining room.
I would move the enlarger to one side and have a long table or cabinet space. A framing/print mounting space is useful.
Cabinets are better than open dust catchers.
I also could not change to work trays right to left. Too old to change.
I will never have a room without water and air filters.