What's the deal with the extra license plate holder on this bumper?

This is a JDM-spec bumper, which means it comes with an integrated license plate holder mounted on the cover. You can have your body shop cover it during paint if you prefer a cleaner look, or leave it exposed—either way works fine.

Does this cover mounting sensors or have any pre-cut sensor holes?

The raw product data doesn't specify sensor cutouts or holes. Before ordering, confirm whether your vehicle has rear parking sensors that would require modifications to this cover.

Will this fit my parking sensor or backup camera if I have one?

This is a solid bumper cover with no pre-drilled sensor or camera holes listed in the specifications. If you run aftermarket sensors or a backup camera, you'll need to have your body shop or installer cut and integrate those during the paint and installation process.