Does this fan come ready to wire, or do I need a relay and thermostat switch?

The fan motor is included and operational. You'll need to source a thermostat switch and relay setup to control when the fan turns on and off based on coolant temperature — that's not bundled with this unit.

What voltage does this fan run on?

Voltage specification is not listed in the product data. Confirm your electrical system voltage before wiring — most aftermarket cooling fans run 12V, but you'll want to verify the motor rating before committing to a thermostat switch.

Will this bolt directly to my stock radiator mounting brackets?

That depends on your radiator and bracket design. The fan shroud and motor assembly are standard 12-inch configuration, but mounting holes and bracket alignment vary. Test-fit against your radiator before finalizing bracket position or fabricating custom mounts.