Will this interfere with the OEM front bumper or trim?

No. This lip is engineered to mount beneath the stock bumper without cutting or removing any factory panels. Verify your bumper has factory underspoiler holes or mounting tabs before ordering to confirm your setup matches this design.

What finish should I apply to bare carbon?

Sand and prep the surface, then apply a UV-protective clear coat to seal the weave and prevent oxidation. A quality automotive clear coat (2K or single-stage) will preserve the carbon texture and gloss. Skipping clear coat will dull the finish over time from UV exposure.

Does this add much weight to the front end?

Carbon fiber is significantly lighter than the OEM plastic lip, which keeps front-end weight minimal and preserves your platform's balance. Exact weight reduction depends on the OEM component you're replacing; reference your vehicle's service manual for baseline specifications.