Will this work with aftermarket bumper covers or lower valance kits?

This strip is engineered for the factory bumper assembly. If you're running an aftermarket front-end package, verify that the grille opening dimensions match the OEM 300 bumper before ordering.

Does this include hardware for installation?

The strip itself ships as a single piece. Fasteners are not confirmed as included — use stainless or corrosion-resistant hardware rated for exterior automotive use, and refer to your vehicle's service manual for torque specs.

Should I prime and paint before or after install?

Most builders prime and paint after bolt-down to avoid paint damage during handling and to ensure a seamless finish with the bumper. Mask off mounting areas before spraying.