The underground complex has been designated, and the last 3 migrant waves (each one only a married pair of dwarves and a kid or 3) have been drafted to be miners. Trained them up on digging the massive tree farm right above the aquifer layer, moving the to the marble harvesting site when they got skilled enough.
After they finish digging the marble layer out, I will have them cut into the caverns and the masons on standby will seal up a large enough area to ensure full access to the complex. I plan on a double-helix rampway leading from the surface down, and will need to do a little construction to fix the empty bits left by the caverns.
The underground complex consists of concentric rings, each slightly larger than the last, spanning 5z total. The uppermost part is a round meeting area, where the ramps from the surface will connect. The next level down will be finished goods storage, while the next 2 will be dedicated to food production, storage, and any other related industry. The 4th level will be dedicated to housing, with some of the apartments looking down into the main commons. The main commons will be the most massive, covering most of the 3x3 embark. 2 walkways will be separated by a magma channel through the middle, and will be filled by pumps in each corner. The center of this area will dip down some more, leading to the forges and smelters, with magma underneath that to power those industries.
Not especially complicated, or anything. But its the first massive, overly complex thing I've done yet, and been working on the designations since I woke up at 7am (now around noon, my time). I'm debating on main the main commons multiple zlevels, using ramps to carve upwards. Should be able to get everything smoothed and engraved as long as I leave the ramps in place.
I figure the noble quarters can do either directly under the magma for the forges, on top of the clown fortress, or over the magma pipes nearby. I'll worry about that when I need to, right now I'm under a severe labor shortage. Don't want too many migrants yet, since the facilities do not exist to house, clothe, and feed them.