Will this interfere with the hood when it's open?

No. The front lip sits below the hood opening and does not extend into the engine bay. Verify clearance by opening your hood with the lip in place before final fastening.

What's the best way to prep FRP before painting?

Sand the entire surface with progressively finer grits to scuff the primer coat and improve adhesion. Wipe clean with a tack cloth before applying your base coat. Your paint supplier can recommend specific products for best results over primer.

Does this require any cutting or modification to the bumper?

No cuts are required. The lip uses existing factory mounting points. Inspect your OEM bumper attachment hardware before installation to ensure all fasteners are present and functional.