I don't do that much sculpting, so take this with a grain of salt, but I'd do this: 1) Make several base-mesh rocks, and duplicate them until you have your wall spaced out roughly. 2) Add a plane that will act as the mortar/concrete that holds the stones in place 3) Sculpt 4) Export rocks as one mesh, plane as another 5)…
I would probably go with option A. using this script for the rocks. Then bake those suckers out normal + AO + an alpha of only the rocks. Finally paint the diffuse(and spec?) colors in PS using the alpha texture to help with selection/masking, rather than using a photo based approach. EDIT: Or you could use photos and the…