To spool:
Wow, that's pretty. And neat. And pretty neat. I only want to suggest a few things, which you may already have planned.
1) First and foremost, your last defense gate next to the trade depot has a flaw. I consider this the most important fix to make, as the only thing more dangerous than no security is a false sense of security. The bridge raises toward the depot, so a building destroyer need only smash the depot to be able to reach and destroy the bridge. Dismantle the bridge, maybe smooth the floor beneath it if you're as aesthetically demanding as I am, dig a 2x3 trench across the hallway, and build the bridge so that when raised a building destroyer can't stand next to it on the same Z level.
2) Do you plan on chaining animals at choke points near your entrance? They're pretty good at spotting kobolds and ambushes.
3) Do you have magma or regular forges and smelters? Because if you're trying for a larger population, which requires a larger military, you will find that using trees as fuel will limit you greatly. Consider either making a metal industry above the magma sea (or a lava tube if you're lucky), or pumping magma up under your metal workshops block.
But I'm curious, did you give your dwarves any temporary quarters while digging out this massive place, or did they simply sleep on rough ground until the job was done?