Do I need the left-side molding too?

This is the RH piece only. You'll need both sides for a complete grille border. Buy the matching LH trim molding to finish the job.

Does this need paint before installation?

Check your current grille trim color first—if it's already painted or matches your bumper, you're ready to bolt on. If you need a fresh coat, prep and paint before install so you don't have to mask around mounted plastic.

What fasteners do I need?

Hardware is not included with this trim. You'll use the existing factory attachment points on your grille and bumper assembly—bring the car's service manual or test-fit before deciding whether to reuse original hardware or pick up new fasteners.