My solutions so far:
Furniture:
* Put doors and statues everywhere around the workshops. Dwarves will see them whilst working and get happy thoughts. Smoothing / engraving around workshops doesn't appear to do anything. Try and keep a varied selection of furniture around and place any artifacts either in your dining room(s) or your statue rooms or highly trafficked areas. If you're lucky enough to get an artifact that can be used in a workshop do so (e.g. artifact mechanism for screw press ; artifact barrel for dyers, etc).
* If a particular dwarf is unhappy, give them something they like (e.g. if they like green glass, put a green glass statue in their room).
Conflict
* Try to predict roughly where battles will take place and put an atom smasher nearby - on my map goblin sieges always appear in the middle of the top part of the map, so I've got an atom smasher near to where the bodies will end up.
-- On conclusion of the battle, z->stocks->body parts -> unforbid -> dump ; z->stocks->corpses->unforbid->dump ; go to the refuse piles containing bones, shells, hair, skulls, teeth and remove the dump (I have separate stockpiles for pretty much everything). Do not "claim" any armour/weapons of fallen enemies yet - wait until the dumping has finished. This should ensure that the bodies lying on the battlefield get cleared away as quickly as possible.
-- I've yet to decide exactly what to do with caged things that can't be tamed. Right now my strategy of building the cages in a honeypot trap and letting a forgotten beast massacre them at a later date is unsatisfactory at best.
The Unhappy Bunnies
* Have a military squad (or several) to place unhappy dwarves in. After a battle or if there are corpses needing hauling those dwarves should be activated, sent to their barracks and not allowed to see bodies and body parts.
* I also have an area where I can isolate dwarves in their military squad - this is an area with 5 rooms which are as nice as I can make them (smoothed/engraved/artifacts) - a dining room, a statue room, a room with 2 separate stockpiles for food and booze that take from the main food/booze stockpile, a dormitory and a barracks. These rooms can be sealed with a door and a bridge.
-- When these dwarves are really depressed, remove these rooms from the burrow, set military alert on and set the military squad of depressed dwarves to station in that area. It can be tricky getting all of them there at the same time but persist (small squads can help)! Once they're there, forbid the door, and pull the bridge to seal them in. You can then take them off station, add the rooms back into the burrow and leave them be. Set them to train if you want, doesn't really matter a great deal - some training in discipline may help more testing needed. They will complain they have no shoulder to cry on but this doesn't seem to stop their stress decreasing. (To make this trickier you should really have some way of preventing them getting cave-adapted but this can be fiddly).
-- A very stressed dwarf (200k stress) will take over 3 years to decrease back down to below 100k - but they can be allowed to wander around the fort as long as there is no body hauling going on. Definitely remove refuse hauling from any of the really stressed regardless.
-- Ideally equip the military squad with metal armour, as then they won't get any negative clothing thoughts.
-- You may find you need more than one military squad and set up like this (it can help to rotate people in and out of squads as they become less unhappy). Currently I have "The Unhappy Bunnies", "The Hares of Despair" and "The Long-Faced Leverets". I'm also running out of synonyms for rabbits but that's a separate issue.
-- You won't be able to completely isolate your mayor or your duchess like this.