Will this light work with my factory bumper, or do I need to modify the bumper opening?

This is built for direct fitment into the factory bumper housing. No cutting or enlargement needed — it slides into the OEM mounting points.

Does this come with wiring harness and connectors, or do I need to splice into factory harness?

Wiring configuration not specified — confirm what your bumper harness setup requires before finalizing install. Some buyers adapt to factory connectors; others run new harness runs.

How bright is the white LED output compared to stock halogen?

LED will be noticeably brighter and whiter than factory halogen. If your other bumper light is stock halogen, you may want to upgrade both for visual balance.