Do I need special fasteners to install these?

These bolt to factory mounting points, so standard hardware compatible with your OEM holes will work. Check your vehicle's service manual for the correct fastener size and torque specs.

What prep do I need to do before painting?

Sand the surface with appropriate grit to create adhesion for your chosen topcoat, then clean thoroughly. Follow your paint system's manufacturer guidelines for primer and finish application over FRP.

Will these fit with aftermarket wheels or lowering springs?

These are designed to clear the factory wheel and suspension setup. If you've significantly widened your stance or lowered the vehicle, verify tire and suspension clearance against the fender extension before installation.