Will this interfere with the factory front bumper sensors?

The center section mounts flush with your OEM bumper. If your vehicle has sensor cutouts in the stock bumper, you'll need to verify clearance during test-fit — the lip may sit close to those areas depending on bumper revision.

Do I need to paint this before installing?

That's your call. Most owners either primer-coat the raw panels before bolting on, or paint after installation once they confirm fitment. Test-fit first, then commit to paint or primer.

Does this work with an aftermarket lower valance or splitter?

Compatibility depends on the specific aftermarket piece — this kit mounts to factory points, so as long as your splitter or valance doesn't occupy those same bolt holes, they can coexist. Measure and mock-fit to be sure.