Ferry RT Naples-Amalfi
 

Will be in Naples for 2 days this September. Want to see the AC by water, eat, walk around a bit in Amalfi and then head back to Naples. Here are a few questions for you. Thanks.
Which ferry company: NLG or Positano Jet
Date choices: Sunday or Monday
Advance tickets necessary?
Rough waters: not sure I want to go, but do they cancel for things like this? Refund if they do cancel due to weather?