I've experimented with my earlier idea with the 7x7x7 layout. I set up 6 'cubes' on either side of 3 wide hallway. I originally wanted to have 6 cubes branch of a central 7x7 cube this would have been more efficient, but I was struggling to figure out how to connect the apartment levels to this central area so I gave up and used a hallway.
It is a very efficient layout. I actually ended up with more space then I knew what to do with, the textile industry being the only one needing so many levels and workshops and stockpiles. Most industries just need 3 or 4 levels and products were churned out at a rate greater then I could replace raw materials. To me, the whole set up looked pretty crap, aesthetics wise. Turns out I really dislike staircases going through the middle of stockpiles and through workshops and in the middle of narrow hallways. I like being able to lock dwarves into their workshops when they go insane and lock and forbid stockpiles to keep dwarves from pathing into them.
Ran into a lot of shortages of stone, with 7 layers of mudstone and using blocks I didn't have enough to build an aboveground fortress with the same footprint as the rest of the fort and nobody likes multi-colored aboveground structures.
Mining wasn't as big a problem as I thought it would be, I just worked one mine at a time, mass dbd'd everything down to the forges when it was done and walled it up. Definitely implement some kind of safety system with that ore chute next time, had a lot of furnace operators killed when ore was being dumped.
I'm sketching out a revised version with no stairways in individual rooms, but I end up tweaking it until it's no longer very efficient and haulers are crawling all over each other to get through workshop doors and whatever.