Formal Night is optional.
Cheers does not work on Carnival's Private islands.
Food is subjective and you'll get many different OPINIONS.
I believe the kids club does feed them. (at least sometimes).
Shorter Cruises tend to be a bit more rowdy, however, 4 days cruise are calmer than 3 days but YMMV.
Ceviche, whole fish, lobsters, 2 beers, 1 margarita = $65. We paid with credit card. Sometimes it is better to pay with pesos on account the vendors set heir own exchange rate or claim they don’t have change.
Mazatlan there is a blue line that you can follow (starts across the street from the terminal).
PV I believe requires a cab to get to the Malecon or the Zona Romantica.
Don’t know about the other ports.
Chat is worthless. If you need to communicate electronically then pay for the social Wi-Fi and use WhatsApp, Facebook messager, or Snapchat. Everything else worked fine.