Do I need hardware to install this, or does it come with mounting fasteners?

The panel itself is included — fasteners are not confirmed as part of this kit. You'll want to verify your truck's original bumper mounting hardware before assembly.

Can I paint this before I install it, or should I wait until it's bolted on?

Paint after installation. That way you can sand any seams or gaps flush with the bumper, then shoot the whole assembly together for a seamless finish.

Will this filler work with aftermarket bumpers, or just the factory unit?

This is engineered for factory bumper fitment. If you've already swapped to an aftermarket bumper, the mounting points may not align — test-fit before committing.