Do I need to replace this every time I pull my header?

Yes. Header gaskets compress under heat and lose sealing ability once disturbed. A fresh gasket each time is the only way to guarantee no exhaust leaks.

Can I reuse the old bolts when I reinstall?

Check your service manual for bolt torque specs and whether they're stretch bolts. If they are, new bolts are the safer call. Hand-tight first, then torque in a star pattern to avoid warping.

Do I need to clean the header surface before installing this?

Yes. Scrape off old gasket material and carbon buildup from both the header and cylinder head. A clean, flat surface is critical for a proper seal—don't skip this step.