@The13thRonin: Which is why I mentioned regular tanned leather. Leather used for protection would most likely not be tanned but boiled before the step of tanning it, the exact process is unknown but the resulting material was supposedly a hard but somewhat brittle material. I think in some parts of Europe it was worn as lamellar armor, but more common in west-europe was the cuirrass, likely because the cuir bouilli gave at least a limited amount of protection against blunt impact.
The argument about 'nibleness' is... not completely rubbish, but as its often understood still mostly rubbish. If a man at arms wanted to be nimble, he would get a brigandine instead of a plate cuirrass. Possibly replace a hounskull helmet for a kettle helm for visibility, but anything below that would almost certainly not have been done to be more nimble. You have to keep in mind that as a soldier in the middle ages, there not a lot of one on one combat. There was a whole lot of getting shot at, poked at by pikes and other polearms and getting run down by cavalry before there was even any hand to hand combat at all, and for none of that your niblety would be much use at all. Archers and crossbowmen intently aimed for formations with less armor and being in that formation would be an absolute hell nobody would be in voluntarily. Games often hugely overstate the encumbrance of heavier armor and give all sorts of contrived advantages to the leather-clad fellow with daggers because they want to strike a gameplay balance, not because of any historic precedent.
The most common protection for the poor folk was quilted cloth, or sometimes coats with densely stuffed horse hair. These are in the mod as the gambeson, aketon and various other items, and they were not actually such terrible protection.
It is also important to note that as EuchreJack mentions by the late middle ages, say end of the 100 years war or war of the roses, pretty much everyone going to battle had at least some form of metal armor. Metalworking advanced had advanced a lot, people became richer and military leaders started to realize the value of professional, well equipped soldiery. Though the vicious peasant revolts in that era did make up for the lack of peasant slaughtering (poor, poor peasants...)
Anyhow, my main reasons for not including much leather armor: Padded cloth armor was far more common, likely more effective and easier to make in larger numbers. Also the weird studded leather fetish game and movie makers seem to have for anything medieval really needs to stop.
@EuchreJack: Most of the one-handed weapons in this mod were generally used as a sidearm. So the daggers but also one-handed warhammers, estocs, arming swords, etc. Longbows are obviously out of the questions but crossbows should be ok (and might be your best bet as ranged weapon damage is not affected by creature size).
You could have them use the lighter onehanded weapons with two hands like this, if your human is 70000 size and your hamsterman 20000 size:
[ITEM_WEAPON:ITEM_WEAPON_SWORD_SHORT]
[NAME:modern arming sword:modern arming swords]
[ADJECTIVE:short]
[SIZE:105]
[SKILL:SWORD]
[TWO_HANDED:40000]
[MINIMUM_SIZE:15000]
[CAN_STONE]
[MATERIAL_SIZE:3]
[ATTACK:EDGE:250:5500:slash:slashes:NO_SUB:900]
[ATTACK_PREPARE_AND_RECOVER:5:1]
[ATTACK:EDGE:9:5000:stab:stabs:NO_SUB:400]
[ATTACK_PREPARE_AND_RECOVER:5:1]
[ATTACK:BLUNT:30:0:strike:strikes:pommel:1400]
[ATTACK_PREPARE_AND_RECOVER:5:1]
This arming sword could be used by any creature larger 15000, but they will get a stat penalty for not holding it with two hands unless they are larger than 40000.
Keep in mind, creatures have a variable size. Length and broadness apply a multiplier to the creature size so a particularly short and skinny hamsterman may be below 15000 size and unable to wield the sword still.
Portable firearms of the time where the handgonne (also called hand cannon) and arquebus (also called hackbut).
The handgonne was basically tiny cannon, either socket mounted onto a staff or mounted on top of a crossbow stock. They were fired in various ways, some over the shoulder, some against the shoulder, against the chest, etc. They were the very first hand-held firearm, VERY inaccurate and and at most a had simple serpentine as firing mechanism (an S shaped bit of metal with a lit fuse on the end, hinged in the middle so the gunner could hold the gun with both hands while firing it). They were almost only useful in sieges and were often used along with a pavise and other sorts of wooden defenses. There is a also some pictures of riders using a staff-mounted handgonne as a mace, which I suppose makes sense.
Arquebuses were a bit more advanced, they had a narrower barrel and a full stock. It generally looked like a shorter musket. It more commonly came with a firing mechanism, usually a snap-matchlock (a small metal arm with a fuse, held up by a spring and released by a trigger), but there are still some examples that just had to be fired just by pressing a fuse to it.
Both of these were used alongside in the 15th century, and it is important to note that these still had trouble piercing well-made plate armor.
Implementing them into DF might be a bit of a pain, the way I did it was to make a ranged weapon with no ranged skill but it confused the game and the handgunners never brought ammo with them.
Well, this post ended up being long. I hope its interesting for someone!