Will this lip scrape on speed bumps or steep driveways?

Front lip extension will lower your approach angle slightly at that point. Verify ground clearance on your vehicle's current setup—measure from the ground to the lowest factory bumper point and compare to any aftermarket bumper or splitter you're running. You can also test clearance with cardboard or tape before committing to a permanent install.

Does FRP stay rigid, or will it flex during driving?

FRP is hard panel construction designed for shape retention. It won't flex like plastic trim, but it will flex slightly under impact—that's a feature, not a flaw. It absorbs low-speed parking lot contact better than rigid carbon fiber or ABS. For track use or heavy curbing, sand and repair as needed; FRP is forgiving that way.

What prep work is needed before painting?

Sand the surface to ensure paint adhesion—standard 220-grit as a starting point, then step up to finer grit for a smooth base. Clean thoroughly to remove all dust and residue. From there, follow your chosen paint system's prep guidelines. The panel is ready; the finish is up to you.