Do I need new bolts or fasteners to install this?

Gasket-only unit. Your existing header bolts work fine—just clean them and reuse them. If they're stripped or corroded, grab new header bolts separately.

Do I need to clean the mounting surfaces before installing?

Yes. Scrape off old gasket material and carbon buildup from both the header flange and cylinder head. A clean surface is the difference between a seal that holds and one that leaks within weeks.

What if I need gaskets for multiple cylinders?

This is a single gasket. If you're replacing headers on all cylinders or doing a full header install, order the quantity you need based on your cylinder count or header configuration.