Do I need gaskets or new hardware to install this?

You'll need a new exhaust gasket at the cat flange connection — reusing the old one risks a leak. Bolts are standard and typically reusable if they're not corroded; if you're unsure, pick up a fresh set of M8 or M10 fasteners depending on your flange spec.

Will this cause a check engine light?

No. This system bolts directly to your factory cat and doesn't touch oxygen sensors, so it won't trigger any codes. The cat does the emissions work; this is everything behind it.

Does the stainless tip need any prep or coating before install?

The tip ships polished and ready to go. No paint or clear coat needed. Over time, heat cycling will darken it slightly — that's normal. If you want to keep it looking showroom-bright, polish it every few months.