Do these require any welding to install?

No welding needed. These mount at factory bolt points and connect to your stock downpipe. Basic hand tools and a few hours get the job done.

Can I reuse my original gaskets, or do I need new ones?

New gaskets are included with these headers. Use them — old gaskets flatten out and won't seal reliably once disturbed. Fresh gaskets ensure no leaks.

Should I apply high-temp coating to the outside?

Not required. Stainless steel resists heat discoloration on its own. If you want a specific finish or maximum heat rejection, coating is optional but not necessary for durability.