Will this diffuser scrape on steep driveways or inclines?

The J Sport profile does extend lower than OEM. Verify ground clearance with your current suspension setup and any added lowering springs or coilovers. Measure the OEM diffuser gap first, then compare to your driveway angle before final installation.

Is the diffuser functional or purely cosmetic?

J Sport diffusers are primarily cosmetic—they deliver the aggressive look of the style. Any aerodynamic benefit at street speeds is minimal. Install this piece if you want the aesthetic; don't expect track-level downforce gains.

What prep and finish should I apply?

Carbon fiber benefits from a UV-protective clear coat to prevent fading and oxidation over time. Sand and prep the surface before applying your chosen finish. If you prefer the raw weave look, apply clear coat only for protection.