Do I need gaskets or sealant to install this?

Gaskets are strongly recommended at both bolt flanges to prevent exhaust leaks. They're not included with this pipe — source them separately to match your 2.25" tube diameter and bolt pattern.

Can I weld this or does it have to stay bolted?

Keep it bolted. The flex section is designed to move, and welding it would defeat that purpose and create stress points that crack quickly.

Will this work if my manifold bolts are stripped or damaged?

The flanges bolt directly to factory points, so if those holes are compromised, you'll need to repair or re-tap them before installation. Test-fit first to confirm bolt alignment.