Well, it was good to have a plan, but the routing was more tedious than I had imagined it would be. So the bottom layer didn't get routed, and the top layer just got some.
The bottom two layers are now glued together. I set the third layer on top of them for the photos:
It's clear that most of the foam has been removed from the two middle layers, leaving bulkheads in strategic places for strength and to prevent oil-canning. The amas will be much lighter now. The for'd and aft bulkheads are situated right under where the akas will attach. The middle bulkhead is roughly half-way between those (I don't remember measuring for it).
I'm still planning to round the top of the top layer (the deck, so to speak) as in the drawing in the previous posting, so with the bit of routing and carving that's been done on its under side, some weight will be lost from that layer as well.