I don't know what your plans are for uncoupling ramps, but I would suggest KaaDee magnets on a bell crank that would swing the magnet out of the way except when you want to uncouple cars. That way you don't get nusance (spelling) uncoupling. 72" off the floor is probably too high to use any of the various manual methods of uncoupling unless you build foot stools to raise you up to a higher level at the points where you will be switching out industries. The overall plan looks excellent. You have a main for some continuous running, plenty of room for scenery, and enough industries to make switching fun.