Do I need to flush the system before installing this condenser?

Yes. Flush the refrigerant lines and receiver-drier before connecting the new condenser. Debris or moisture left in the system will damage the compressor and reduce cooling performance.

What refrigerant does this condenser use?

Confirm your vehicle's refrigerant type in your service manual before charging. Most Crown Victorias of this era run R-134a, but always verify before opening the system.

Does this come with new O-rings and seals for the connection ports?

The condenser assembly ships with the unit itself. Source fresh O-rings and seals separately—they're wear items and should be replaced any time you open the AC circuit.