Will this affect ground clearance or create a scrape risk?

The front lip extends minimally from the stock bumper profile. Your scrape risk depends on your current suspension setup and driving habits. Verify the lip's extension against any aftermarket suspension modifications you've already installed, and drive conservatively over steep driveways or speed bumps until you're comfortable with clearance.

Is FRP rigid enough for daily use, or will it flex under pressure?

FRP is engineered to resist flex under normal road conditions and light impacts. It won't sag or rattle like some plastic trim. For protection during parking lot incidents, consider adding a protective film or parking with caution — FRP can crack if struck hard enough, but it's far tougher than OEM plastic.

What prep work is needed before painting?

Sand and prep the surface with appropriate grit before applying your chosen basecoat and clear. Ensure the lips are clean and free of dust. Check fitment to the bumper assembly before painting to avoid rework if adjustments are needed.