OP:
1) Just ranged can work well if your guys are any good. exception might be large inorganics, maybe mb/fb style thing so always useful to have a melee backup.
2)Sparring gives good training and doesnt seem to use any skills. Demonstrations can give teaching under the right circumstances. it appears to cap out round mid-levels from other posts here.
Teacher needs teaching, organisation and a skill to teach. the higher these 3 are the better he teaches, proportion appears unknown.
Student needs student and concentration. maybe focus stat?
the whole thing is a little mysterious but theres been a few tests done embarking with tailored teachers with favorable results.
teachers sometimes teach stuff they suck at......seems unavoidable.
3)i usually have marksdwarves in own unit for logistics when giving them orders...i.e. i know that squad are all ranged.
In order to use an archery range you must assign the squad to train there through q,t. However they also need to be assigned a barracks before they actually use it. If set to train at both they hang out in the barracks according to the number required by the schedule and any spares eat/drink/sleep/shoot at range.
While in the barracks theyll train the usual combat range and hammerdwarf for crossbow melee
my metal uniform is:
Helm, Leather Cap, Leather Hood
Mail Shirt, Breastplate, Leather Cloak
Leather Mittens, Gauntlets
Greaves
High Boots