Do I need to replace this gasket if I'm just removing my headers for cleaning?

Yes. Header gaskets are single-use — once you break the seal, you lose compression at that joint. Install fresh gasket every time headers come off to avoid exhaust leaks and rough running.

What hardware do I need to bolt the header back down?

Refer to your vehicle's service manual for the correct fastener specifications. Gasket comes alone — you'll need the proper bolts, washers, and torque sequence from your manual.

Should I use sealant on top of this gasket?

Gasket is pre-formed to seal without additional product. Some builders apply a thin bead of high-temp gasket maker for added insurance on older engines, but it's not required — test-fit the gasket first to verify it sits flush.