If the plant runs on industrial Ethernet, does this drive drop in directly?

PROFINET and EtherNet/IP are onboard, so the 6SL3230-3YE10-1AF0 is a native node on a PROFINET or EtherNet/IP network with no gateway — it fits TIA-managed lines alongside the G115D distributed drives. The C2 filter is built in for Category C2 sites, and DC terminals allow a du/dt filter or braking module.

When the cabinet needs C2 EMC compliance, is an external filter required?

No. The C2 filter ships integrated and factory-tested, so water-treatment and HVAC plant rooms meet Category C2 without an add-on module or extra commissioning step. An unfiltered variant would push that cost onto your build.

What overload applies to 0.75 kW pump and fan duty?

Pump and fan loads are variable-torque, so the drive is rated at Low Overload: 110% of rated current for 60 s. At 0.75 kW that is 2.1 A continuous, in a 73 x 232 x 209 mm IP20 FSA frame.