As for the shields, I thought wood would be better, but seeing that it could be used as a weapon then Steel or Iron should be the choice, not Copper. The reason being that the mass of Copper is higher than Steel.
For shield bashing, only weight should matter - i.e. copper should be slightly better than other metals, but it's still about 98% irrelevant, since shield bashes are a very weak blunt attack. Even with a metal shield, they'll be barely more efficient than a bare-fisted punch and it's a very rarely chosen attack anyway. If your priority is cheap production and low encumbrance, use wood or leather, if you must be wary of fire-wielding attackers, use whatever metal is plentiful (can be adamantine, which is very fire-proof _and_ light). Optimising for shield bashes should almost never be a concern.
- Leggings (5 * Adamatine wafers)
- Greeves (6 * Adamatine wafers)
According to the wiki, leggings and greaves are both [SHAPED], so cannot be worn with each other. A mail shirt and high boots already cover all of the lower body among them, so the most attractive choice are greaves, which should offer extra protection against blunt attacks.
Adamantine is a great armour material, but not spectacularly better than steel, so i tend to emphasise weapons and trap components. With 750 raw, you can of course equip a dozen soldiers in all blue and arm a dozen traps with three serrated discs each, and make a dozen each of every edged weapon and still have some left to play with.