About the weaponry, One way I can think of to balance the disk launchers is to make them absurdly heavy. A dwarf with a disk launcher and carrying serrated disks probably couldn't move very quickly at all, so you should/would have to make sure that they were positioned beforehand.
Oh god when I tested them it was clear just how nightmarishly heavy a full load of ammo was. The weapon itself is fairly light, but the ammo would indeed require the soldier to be in position beforehand to get the most out of him and his weapon; they reloaded slowly as well, also due to the weight the dorf was lugging around (hence why the Civil Defense Corps' kit was so stripped down: They could shoot faster because they weren't as encumbered, even though it was at the expense of protection.) They did move considerably faster with bone discs, but they were only able to hurt something not wearing any clothing/armor whatsoever beyond a bruise at most.
For example, a bone disc will gut a badger, but utterly fail to hurt a lightly armored goblin barring a lucky hit that may cause a skin tear or nasty bruise.
I never got a chance to fort mode test the railgun, but I imagine the ammo will probably be pretty heavy for them too.
The same thing could apply to native railguns. Also about railguns, magnetite bars would be less than effective, as the propulsion for a railguns comes from a chain of electromagnet that activate in sequence, copper wires would be far more effective.
I think I'm getting carried away.
You're thinking of a coilgun. Those use a series of magnets down the barrel whereas for us we're using two parallel conductive rails and have a considerably slower rate of fire. The weapons Ballpoint and Parasol have are more likely misnamed coilguns though and more in line to what you're thinking of. I thought of magnetite rails because they're already magnetized, plus didn't you get why magnetite was chosen besides that? Railguns use magnetism? Magnetite? Geddit?
.... I know, I'm not funny...