Well, the lessons of the day are that I think killing HFS without cheating might be doable.
If you can kill off the initial flood with cave-ins or the like, then you're only going to be facing a random couple of demons floating in occasionally, which a very good military with plenty of expendables should be capable of handling.
After that, screw obsidian casting, you can pretty much pave HFS. I don't get any "Too close to edge" warnings when I put up walls underground. It seems like you can just put floors over the glowing pits, and build walls along the edges outright.
(The roads to Hell may be paved in good intentions (by which we mean adamantine), but the roads IN Hell are paved in marble!)
Okay, I'll try if not bored beforehand.
The pack of war elephants is VERY effective.
Fb comes in, kills dwarves left and right... then an elephant notice it and brainstomps it. This pattern repeated with the last 5 FB (sometimes it takes 2 or 3 kicks, tough). Guess it's the blunt damage.
Still no male Cave Crawler, goblin civ nearby, so I'm keeping my fingers crossed for a siege.