The six cloak uniforms are a bit of a blast from the past, just because they can wear them doesnt mean you should really bother. When outfitting your young military this means your militia commander is going to claim the first six cloaks from your leatherworks, you could have covered more than half a squad with that leather. In the early game i'd strongly advise against this kind of duplication, especially if you dont yet have a steady leather supply.
Which pieces you make depends on the ratio of metal:leather you want really. Anyone who is expecting to be hit with weapons of any kind should have metal armour, leather is better used for animal defense (and then only smaller animals !not badgers!)
Mail shirt and helm should be priority. These two cover the main insta-kill hit locations (and mail shirt covers more than breastplate so should come first)
Next up is your choice, but for melee warriors you probably want mainly metal. If you have high boots then you can do chain leggings and high boot, if you only have low boot then you should do greaves instead of chain legging (again for coverage reasons, leggings + low boot leaves a gap). High boot and greaves also works fine.
Gauntlets for hands and you just have breastplates to add over the mail shirts
You can also put some leather under metal pieces to add protection (mainly vs blunt).
Leather trousers can go under greaves, leather mittens under gauntlets, leather cap under helm. You can put leather armour (body armour) under a mail shirt but not under a breastplate. If you want faster dwarves you can swap metal pieces for leather and more layers, but no amount of leather is going to save dwarves even from a copper edge or the teeth of something larger-than-dwarf.
ALWAYS have a leather hood and leather cloak on every soldier. The hood is the only item in the vanilla game that is throat armor (also face parts like lip/cheek), it sucks, but what can you do? The cloak is also the only armour piece for a bunch of weird locations like fingers and toes.
Summary: My Recommendation
Leather Hood, Metal Helm, Leather Cap
Metal Mail Shirt, Metal Breastplate, Leather Cloak
Leather Mitten, Metal Gauntlet
Leather Trousers, Metal Greaves
Metal High Boot
Oh, and shields, always give em shields (wood is fine)
Incidentally, My main use of leather armour is on the 10 or so squads of drafted haulers. They never train or fight, its just a convenient way to armour your seige cleanup crew while letting them run away fast