Long up/down staircases are such a bad idea that I had to make two, side by side. But I wasn't planning on developing around this shaft, I was just probing for a cavern floor and magma. The starting bunker was designed to be converted to a barracks after getting everyone moved out, but it's still being used as the main entrance, and workshops and apartments are still clustered around this 90 level shaft to nowhere. So now stoneworkers that could be doing something better are making 90 hatches, 2 for every other floor.
At least the straight line route keep everyone off the freight tracks; no matter how crowded the passage gets, it'll still be better than the spiral path. At level 91 I found warm walls, at lvl 92 I found a warm floor, so magma will be ready for my underemployed metalworkers. I'll make them slave in the hell workshop until they develop some skills before I think about bringing the magma to them.
The only defense I have right now is to lock up impenetrably tight, though I'd sacrifice my aboveground assets to do it. My militia is undertrained and underequipped, and a trap defense system is something I'll probably have to improvise while in lockdown. There's no iron ore here, but there is silver, so everyone will get hammer experience whether they like it or not. That should be enough for the first likely enemies, zombies and necros. Well, not counting the cave swallow people downstairs, but my militia has been handling them barehanded just fine, so there is hope for them.