After playing mostly ridiculously timidly, in the current fortress, partly because I messed up early on and am not entirely happy with my fort, I've been playing completely recklessly. Anything remotely hostile, and I charge it with everything. That has included forgotten beasts, undead invasions with necromancers, and lots of things like giant cave spiders, blind cave ogres, blind cave bears, and the usual garbage/meat like troglodytes, crundles, dralthas, trolls, etc. Oh, and fire imps and magma crabs constantly setting stuff on fire whenever they get out.
In one funny moment, my militia commander was shooting at a magma crab, and was in steel armor head to toe except didn't have a helmet. So a glob of lava hits him right in the head and instantly kills him. Lol.
I have gone through about 10 expedition leaders, and one of my major industries is building coffins. Despite this, I've just hit 50 citizens and am a barony. I keep getting flooded with migrants, although I'm not sure why anyone would want to live here.
Also I just dug straight down until I hit magma without taking any effort at all to secure the caverns. So my access to the lower level is currently through an absurdly large 25+ z-layer cavern, and much of the 3 square stairway is surrounded by nothing but empty air and a huge drop. Whenever anyone encounters so much as a crundle on it, there's a good chance they immediately dodge off into thin air and splatter 20 levels below. At the bottom, there's a gorefest full of random body parts and blood everywhere.
The current military is actually pretty good, with deaths being rare, although everyone in it has the "doesn't really care about anything anymore" tag.
I'm trying to make the fort a little safer now that I'm not about to die at any moment, but it's a lot tougher to retrofit a fort to be secure after you built it completely recklessly than to do it right in the first place. The major thing (I've installed drawbridges and secured the top part pretty well now) is to bypass the completely unsalvageable "Stairway of Death." This is trickier than I was hoping, partly because of an aquifer and partly because of the ridiculously unwieldy huge cavern it's in.