Do I need to install a new gasket or use old ones?

Use a fresh gasket set when you bolt this on. Old gaskets crush and won't seal properly against new flanges.

Will this work with my stock exhaust manifold bolts?

Factory mounting bolts work fine here — the header uses the same bolt pattern at the cylinder head. No special hardware needed.

Does this need to be painted or coated before install?

Stainless won't rust bare, so paint is optional. Some owners wrap headers to reduce underbody heat. If you decide to paint, prep with a stainless-compatible primer first.