Do I need new gaskets or clamps to install this?

You'll want new gaskets at the cat connection point—reusing old ones risks leaks. Clamps and brackets are included with the system; verify fitment before final tightening.

Can I weld this or does it need to clamp to the cat?

System is designed to bolt at the factory catalytic converter connection. No welding required; bolted joints give you the option to service or replace later without cutting.

Will this system last if I live near the coast?

Stainless steel resists corrosion far better than mild steel, so salt and moisture won't eat through it the way they would a carbon steel setup. You still want to rinse it periodically if you're in a heavy salt environment, but it's built to handle it.