Do I need new gaskets and bolts to install this?

Yes. Use new header gaskets at the cylinder head flange and new studs or bolts rated for exhaust manifold duty. Reusing old hardware can cause leaks once the header is torqued down.

Should I ceramic coat or paint this header before installation?

Stainless doesn't require coating, but you can paint or ceramic coat it if you want heat protection or aesthetics. If coating, do it before install and let cure fully per the coating instructions.

Will this fit with my stock exhaust system downstream?

This header bolts to the factory ports and connects to the rest of your exhaust at the collector outlet. Verify your current exhaust piping diameter and exit point match the header outlet before purchasing.