If you want to add to your signature you can navigate to it from the menu (3 horizontal bars, top right): Account Settings, Settings Area, Signature. But using this link is much quicker https://boards.cruisecritic.com/settings/signature/.
It's a closed loop cruise, as long as the passport is valid until the end of the cruise it should be fine. One can also travel with an official birth certificate and government issued photo id that includes date of birth.
Celebrity has this article on closed loop cruising, https://www.celebritycruises.com/blog/closed-loop-cruise.
Sad comment on our culture that only selfish motives are being attributed to this passenger. Has no one considered that the carryon may have contained, as many do, necessary for life medication?
Old San Juan is a favorite. A lot of history, interesting fortifications, blue cobblestone roads, interesting architecture, public sculptures, several interesting museums and galleries, good food. A really nice sail in / out.
What you need is dependant on data only you have. Complete the questionnaire as accurately as you can and it should tell you if you need a visitor visa.
Personally, if I had any doubts I'd consider obtaining a visa.
As long as the vessel is leaving the country it shouldn't be a problem. It's similar to the situation if one flew into YVR and caught a connecting flight to Anchorage. The connecting flight flys over Canadian territory without issue.