I have heard many times that bone and leather is crap compared to at least copper no matter what the bone and leather is in regaurds to quality.
Leather and bone is better than clothes, just.
Helmets and sheilds may be the best armor, but it depends.
A wooden sheild will stop attacks as well as a steel, but wood will burn I beleive.
Same for the weapons, masterwork copper is better than lesser material artifact.
High skill trumps all but the absolute best.
Webs= Dead mele dwarves in nice addy armor.
Deadly gas and dust will kill as if they were naked if it is actualy "deadly" dust, it could just make the dwarfs nauseous.
Thats some of the junk I learned by lurking.
I know that leather and bone is crap, I've heard that they are not much better, compared to clothes , it's just that they weigh less (I think) than metal armour, and if metal armour won't protect my dwarves, against forgotten beasts, then I'm better off with faster dwarves.
I always give my dwarves a shield, that's the easiest and best you can get, early on, I seem to remember that wooden shields won't burn, when blocking fire, but I will keep an eye on that.
Shame about the bone axe, reading Garath's post, I wanted to give it to an axedwarf that likes reindeer bone, but I don't even have one, might still give it to my vampire once she serves her sentence, and before I lock her in for eternity.
bonus question 2: yes
Alright, armor vs forgotten beasts... well, it depends. Good armor will definately protect against bites, stings and such. Stomps and other 'blunt' attacks are another thing. When a creature a few times bigger than an elephant (but without the padded feet) stomps on your leg, armor is not going to help much. It was one of the reasons why web spitting FB are so annoying. An immobile dwarf gets automatically headshot, which against a FB stomping means dead, but Giant Cave spiders sometimes happily munch on an immobile dwarf head covered with a steel helmet for ages without getting through with their bite. Any clothing or armor will protect body parts from infections by dust or blood syndromes and such, though some things can't be covered (I think, can't tell them 'hold your breath' either)
Even a copper helm can protect a dwarf's head from a Giant Cave spider bite, but when another dwarf got a bite from a forgotten beast, its head just flew off, so that's why I'm asking, if iron or steel helm can protect a dwarf's little head, as I'm not sure, they are worth the resources there, they might serve better on the ground forces facing goblins.
Eyes and lips, definitely can't be covered, I had my run in with forgotten beast syndromes, so I'm mentally prepared for the worst, though I wasn't sure if they just ignored armour, or spread from uncovered body parts, I guess that doesn't make much difference, except for civilians running trough forgotten beast extract.