A suggestion for small arms.
Not many hand weapons to choose from in game. Maybe a modular system for hand-held weapons would add some variety.
Start with a basic receiver, firing some sort of intermediate universal round (think .30 carbine: big for a revolver, small for a rifle, adequate for protection at 200m). Lore-wise, a portable railgun makes the most sense, as punch, range, accuracy, and rate of fire would be controlled electronically and limited by the construction of the barrel. Add separate barrel, stock, scope, and magazine parts to turn the heavy pistol core into a rifle or MG. Not practical for fighting wars, but the universal and modular nature of the system is plausible for frontiersmen who primarily need to kill charging animals at close to close-medium range. If everyone's gonna be using the same weapons components, this would make the most sense in terms of story. Sort of a 22nd-century Kalashnikov, but much more versatile.
Balance is easy. Depending on the stock and barrel length, a shorter configuration can be made easier to aim and a longer configuration more controllable in sustained fire. Shorter barrels give more rapid fire, longer barrels more punch (and recoil) at a lower rate. The stock enables auto-fire but reduces maneuverability and increases recoil control. The scope forces single shots in aim mode.
Ammunition weight would be negligible and magazines wouldn't need reloading (tiny pellets), but the battery packs would be the primary constraint, with shots of higher power draining them at a higher rate. And of course, bigger weapons (and more ammo) would take up more space in the player's inventory.
A similar system wouldn't be hard to adapt for explosives (grenade launcher, rocket launcher, missile launcher).
So that's my suggestion for small arms. It would add a little more variety to the shooting mechanics.