My tree-fort is mostly built up now. 5600 blocks in use, mostly to "floor" (bridge actually) over quite a bit of the map to provide the required ceiling over beds, tables, chairs and coffins.
Dwarfs can live in trees, but you quickly run out of things to do. Even with the multi-log trees of .40+, building material is limited if you don't dig (one log gives one block, making blocks is mainly for aesthetics, bookkeeping and for allowing caravans to carry logs). Furthermore, farming above-ground is tricky since it requires irrigation and there can be biome changes when going up far enough: my map is temperate on the ground and up to ~ z+8, mountain and thus un-farmable above the treetops. Even more annoyingly, natural trees don't mesh well with dwarven industry - few trees have enough branch space for a 3x3 workshop let alone a trade depot, and twigs, which are pretty much all over a tree's fringes, hinder access.
Consequently, most aboveground stuff was eventually stuck in a jumble of artificial wooden constructions, several z above the ground.
Weirdnesses: once again, i got a moody dwarf without digging a single tile. Don't know what allows "discovering" tiles without striking the earth, but i've had it happen in in several no-digging embarks. Since it was a starting dwarf and a jeweller, i decided to dig up a raw gem after all and walled off the mine thereafter. Of course, no gems were found before striking the first cavern, so there were a few more moods after that.
Around year 20, the elven caravan hiccupped: they wouldn't trade because they "hadn't finished unpacking" which afaik meant one of them got stuck off-map, i.e. got spawned but failed to enter the map proper. While this was bad enough, it got worse: the human caravan
also got stuck, with no unit becoming visible at all. Suspecting that my map entry had gotten bugged, i blocked the place with raised bridges and made a new entry point. The dwarven caravan arrived and traded without issue (and took the spoils of a full year of industry back home: 1,15 Million ☼ in food, crafts and old clothes). In mid-autumn, several human merchants showed up and turned berserk, a few non-violent mad ones entered the map as well. Somewhere in all this, some grown-wood items showed up - and right enough, the following spring the elven caravan showed up again. Seems like the missing elven merchant got unstucked by the human meltdown. There are several tiles near the edge where my dwarfs have to crouch down and crawl, suggesting there are either several "phantom" units, or a phantom wagon
There are still a bunch of untouchable, merchant-marked items around, so the human caravan still has stuck units in place and is probably permanently borked.
A dwarven child got both hands broken in a fall; looking at the place he landed, he was probably playing on the minecart track 11 z above-ground and dodged off. Interestingly, he got positive "put on an exceptional/supreme item" thoughts - when he was sutured/splinted with exceptional cloth and a masterwork splint. Yet another perk of healthcare!