Do I need to use a gasket or sealant with this clamp?

No. The v-band design creates a metal-to-metal seal when tightened. No gasket, O-ring, or sealant needed.

How tight do I need to crank the clamp bolt?

Tighten firmly by hand until the flanges are fully seated and won't rotate. Over-tightening isn't necessary and can damage the cast body—snug is the target.

Can I use this same clamp after disconnecting it once?

Yes. The v-band surfaces are reusable. You can disconnect and reconnect multiple times without compromising the seal, as long as you inspect the flanges for dents or nicks before reassembly.