Will this cover fit over my existing bumper, or do I need to remove the OEM piece?

This is a replacement cover designed to fit the factory mounting locations. You'll need to remove the OEM bumper to install it. Check that your vehicle's mounting points align with the cover before purchase.

Does this bumper have pre-cut openings for fog lights or sensors?

The raw product data does not specify fog light cutouts or sensor holes. Verify your vehicle's OEM bumper hole locations and size before installation. You may need to trim or drill openings to match your setup.

What's the best way to prepare this for paint?

Sand and prep the surface with appropriate abrasive before applying your chosen finish. Follow your paint supplier's recommendations for primer and topcoat adhesion on FRP.