Does this cover fog light cutouts, or will my lights still show?

Fog lights remain visible and functional — this lip sits below the bumper opening and doesn't obstruct lighting.

What do I need to do before bolting it on?

Test-fit first to confirm alignment with your bumper. The matte black finish is ready to install as-is, or you can sand it down and paint to match OEM color before mounting.

Will this interfere with a lower valance or splitter I already have?

Mounting method and clearances not specified — mock up your setup before committing fasteners. If you have existing splitter hardware, verify spacing at the attachment points.