Activated charcoal for the black won't give you black/grey suds at 1 tsp PPO. I can send you a bit if you'd like to try it. http://www.craftserver.com/forums/showthread.php?t=69120&highlight=black
I've only used powdered sheeps milk that a friend in Scotland sent me. I also used powdered butter in a batch with it and it made the most fantastically dense & creamy lather ever!
Both sites that I love to look at. Cyndi Muller's site has some great stuff, even the stuff not related to soap. Susanne makes some beautiful things also and has some great info on her site. She is in the Netherlands.
I know of someone who made her own molds from these directions. A little larger than what you want, but I'm sure the size could be tweaked by your carpenter to fit your needs. http://www.chestnutfarms.com/Soap_and_supplies/info/mold_plan.html
My first try didn't go so well, but after that one it was clear sailing. Could have been the FO I used, because it separated badly. I rebatched that first one one and tried again. I'm now using a bar that I made months ago, and it is really nice.
wow...that's a piece of art! and STRAIGHT dividers...what a concept. how deep is the mold itself? possible to do 36 bars in there pouring it full and cutting horizontally?