Its interesting to read some other peoples takes on this. I have typically used full steel armour with replace clothing set, resulting in no clothes being worn. Ive recently been considering trying to get my dwarves to wear hoods cloaks and possibly mittens and socks as well.
I would have said that uniforms do require 2 boots to be listed but I tend to assign every item manually anyway (and doing so requires 2 x boots and 1 left 1 right gauntlet to be equipped/listed) so possibly a uniform set with 1x"gauntlet(s)" 1x"and boot(s)" does result in a set being worn.
Ive read the wiki page on layering. Im wondering, if one manages to get a dwarf to wear under+armour+over say, and that this requires equipping in a certain order, then as soon as a clothing item wears out and requires replacing, if problems might ensue, with I would imagine under items proving the most troublesome in this regard (since they might need equipping first before steel armour layer). I hope the poster who says that equipping armour/clothes in a certain order has been "fixed" is correct. I need to test this out.
I tend to try to equip every dwarf in my fortress with full steel, and recently I find myself wanting to move dwarves between squads which seems to have some unexpected undesirable and somewhat random effects on the items a dwarf is wearing (this may be due to my failure to understand/plan properly), which has resulted in a dwarf ive moved between squads getting nekkid and chucking a paddy. Thats half the reason id like full clothes coverage underneath full armour. The other half being what I hope/beleive/have read is extra protection from wearing cloaks and hodos in addition to full steel armour.