I found that the average dwarf peasant with no skill in Armor User can wear the following uniform without being slowed down and still have some margin of error for item hauling and whatnot.
Metal helm, chain shirt, Leather Armor, metal Gauntlets, chain leggings and metal low/high boots. Also a wooden shield and copper warhammer. If you have metal high boots, you can skimp out on chain leggings and substitute leather leggings, since the legs will be covered by the chainshirt and boots. Either way works and everything is still covered that way. Once you start getting into greaves, breastplates, multiple chain shirts, metal shields, they start to get slowed down without training.
With the current version, attackers (at least intelligent ones like goblin soldiers) will specifically target any body part not covered with armor 9 times outta ten. If every body part is armored, they'll aim for the lowest quality part of the armor or the thinnest. So they like to go after feet, the head and hands, and not so much like legs that have overlapping chain shirts and leggings. Also 'twisting' damage is currently overpowered and bugged, so even if the armor stops an attack, the force will transfer and can injure anyways.
Also I found leather and silk protect better than cloth. Cloaks also help protect the neck and other odd parts like the mouth. So clothing choices can help protect your dwarves too. Another thing is that Armor User helps determine the effectiveness of armor when deflecting attacks, so your armored and untrained haulers don't benefit from armor as much as a trained soldier. That doesn't change anything, but it's something to keep in mind.