Do I need to replace my catalytic converter or can I reuse the stock one?

This is a catback system, so it bolts directly to your existing cat. Reuse your stock converter unless it's damaged or clogged.

What hardware do I need to complete the installation?

You'll need gaskets and bolts to mate the catback to your converter — these are not included. Check your local parts supplier or refer to your service manual for the correct specifications.

Will this rust if I don't paint it?

Stainless steel resists corrosion on its own — no paint or coating required. You can use it bare or polish it for extra shine if you prefer.