The one real near-fort-destroying tantrum spiral I had occurred in a rather challenging situation where I started out in a Terrifying glacier biome with the only plus being a volcano.
Basically dwarves kept getting killed by blizzard men and wolves (mostly migrants though, luckily), and I was spending so much time on basic survival type stuff (like burying the corpses before murderous ghosts could appear, getting water, etc) that I wasn't getting decent dining halls or sleeping facilities. Burying corpses was particularly challenging since dwarves would run outside to retrieve a corpse and immediately get killed by something. As a result I had a few hauntings despite my best efforts.
Finally something kicked off a tantrum spiral and nothing would stop it (certainly not just giving people a few months off from work). In the middle of it some migrants arrived and after a while the 80 or so original dwarves had almost completely killed each other without doing much damage to the migrants, luckily. I was left with about 20 dwarves, most of whom didn't know any of the previous inhabitants.
Legendary dining halls seem to be really easy to create. All you seem to need is a 10 x 20 room with smoothed walls/floors and enough stone tables and seats for everyone.
I always build 4 beds immediately on embarking (if the area has no wood I bring at least 4 logs along, they're cheap) then make them into a dorm room even if the "room" is actually just a corner of a larger utility room. Even with beds in a crappy room they seem much happier than sleeping on the floor, though I have had some female dwarves get scandalized by shared sleeping arrangements.
My regular private bedrooms are only 1 x 4 and they seem pretty happy even with just a stone cabinet and chest. The fanciest I've really gotten is making the cabinets out of gold. I don't think they actually need even 3 x 3 worth of space, they just need one or two really expensive bits of furniture and smooth walls. Basically space seems to be worth much less than a small amount of fancy crap.
(I think my tantrum spiral occurred when I had 80 dwarves but they were all still sleeping in one big dorm area with no decent dining hall.)
I also try to create a walled-in above ground statue garden to help avoid cave adaptation, but it doesn't totally work because some dwarves just don't seem to like visiting statue gardens. Not sure how much happiness they really get from statues though.
Also, until the food requirements came along, I'd put all non-dog/cat animals in a cage at the entrance to the dining hall. Most of my dwarves were constantly "comforted by a wonderful creature in a cage recently".
Also if you're lucky enough to get any artifact furniture always build it in a high traffic area like the dining hall entrance so everyone will get happy thoughts. If not just build expensive doors, chairs, etc in the dining hall.
Also keeping all of them busy most of the time helps I think because they don't get as much of a chance to all become friends with each other. If everyone in the fortress is friends with everyone else then you're screwed.
Does anyone know if there is some way to display artifact non-furniture like artifact rings, loincloths, etc? I always hate it when they create a totally useless artifact that I can't display or use.