Will these trim pieces cover sensor or parking assist holes in the factory bumper?

No. These grille trims bolt directly to the existing bumper structure. If your bumper has sensor cutouts or lower valance mounting points, they'll remain visible. Verify your specific bumper layout before ordering.

Do I need to paint these before installing them?

That's your call. They ship in raw finish, so you can paint them to match your bumper color first or install and paint the assembly together. Either approach works—test-fit before committing to paint to confirm alignment.

What fasteners secure these to the bumper?

Mounting method relies on factory attachment points, but specific bolt size and fastener count aren't detailed in the specs. Grab your service manual or test-fit the trims to confirm what hardware your bumper uses.