That last question was towards thedoublestrafe, I think, but, for me:
I set them to train on a range (for at least part of the time[1]). Ensuring that there are enough individual ranges with Training set up on them for each to get a go (should they so wish), and as for the setup of the military units concerned, I forget what I do, but it's the same as I do for melee-troops to get them to Melee-train (weapon and ammo-assignment, aside).
I honestly don't know what's causing your trainee-freeze, beyond all the obvious things, except that there's probably one thing amongst all the "so obvious I don't even think to ask it" that's just happens to be so unobvious to you. And I'm wracking my brain trying to work out what to say, beyond what's been said so far. Sorry, not being very helpful, at all.
(Oh yes, and you also ask about bolts: I tend to assign both metal boats for 'proper' use, once I have some at hand, and wooden and bone bolts for training. I may make the latter both training and combat, if there's not (currently) enough of the former to equip them all. Quantities, I can't recall, but whatever the default amount is, probably. My wood/bone bolt stockpile usually sits on the level below the range[2], while my metal bolt stockpile is (or stockpiles are) set somewhere near the central hub of the fortress, on, or close to (either up or down) ground level, handy for resupply when out there on the battlements, or other ambush bunkers, actively seeing off enemy. I tend to not have containers assigned to these stockpiles, so I get an immediate view of need, inefficient as it might be (once stacks have been converted to single bolts, especially).)
[1] When they've attained such a high quality of training that they're actually destroying training bolts, regularly, in my "low ammo loss" design, they're changed to wrestling/melee training. Or back to that, if I gave them a little wrestling training before I could equip them with enough weapons, quivers and training bolts to make range-training viable.
[2] Part of the "low ammo loss" design, that's where all bolts that don't hit a target fall anyway, and where they can get resupplied from when they need some more while training, a simple stairwell level or ramp away.