Does this need a new gasket between the cat and pipe?

Have a fresh gasket on hand when you install — reusing the old one is asking for a leak. Pick up a standard exhaust gasket when you grab this system.

Can I install this myself with basic hand tools?

Yes. Unbolt the old system at the cat connection and hangers, bolt this one in. Jack, socket set, and a friend to hold it level is all you need. The factory mounting points line up, so no improvising required.

Will this affect my check engine light?

Not if you keep the O2 sensor in the cat. This system is a direct bolt-on replacement — no tuning or sensor relocation. Leave everything upstream of the cat alone and you're good.