Will the three pieces install as one unit or do I need to assemble them together?

Each piece bolts independently to the factory bumper. You'll position the center section first, then attach the left and right splitters to create a seamless front lip. Alignment at the seams is straightforward when you follow the factory mounting hole pattern.

Does this interfere with the bumper's lower trim or air dam?

This lip sits below the factory bumper line and is designed to clear existing trim. Check the gap between your bumper's lowest edge and the ground before installation to confirm clearance with your vehicle's ride height.

What finish should I apply after receiving it in raw FRP condition?

Sand the primer surface and apply your chosen base coat and clear coat. Use standard automotive paint prep and finishing techniques to match your bumper. Some owners also choose to seal it with clear protective film if the vehicle sees track use.