Each weapon system unit boosts its range by 4,065m and (can someone put in the full power provided at tl4? Thanks) power. They provide 1800kg of mass each.
Energy attacks from these systems cannot target individual creatures or vehicles, only ships. Attacks also cannot fire through astral bodies and hit the target on the other side.
The power of the shot can be adjusted to suit your taste, but keep in mind that the maximum range displayed on the designer is the real max range. As the energy delivered to targets drop off signifigantly, tuning the power upwards can allow a ship to damage targets even at very long ranges.
A good rule of thumb for powering these systems is one power plant can fully power a weapon system or power 2 systems at half power. However as powerplants become far more efficient at higher TLs, you would require less.
Weapon systems require TL4 and used to require Cryo Heat Sinks to construct. Now they use Heavy Weapons, one per Weapon Unit.