Do I need to prep and paint this before installation?

Yes. The diffuser Requires Surface Prep, which means it has a base coat but no color or clear coat applied. Sand the surface lightly and apply your chosen finish before mounting. This also ensures a factory-quality appearance that matches your paint.

What fasteners or hardware do I need?

This assembly comes as the diffuser panel only. You'll need to source fasteners appropriate for your vehicle's mounting points. Check your service manual or original bumper attachment method to determine bolt size and quantity required for proper installation.

Will this fit if I have aftermarket exhaust or diffusers already installed?

Rear lip diffusers mount to the bumper structure, not exhaust components. As long as your bumper is factory or a compatible aftermarket unit, this diffuser should fit. If you've modified the rear bumper area significantly, verify clearance with your existing setup before purchase.