Welcome to Cruise Critic. Recommend you ask/research on the Italy ports of call forum. Lots of great info available that you'll find useful. Link:
https://boards.cruisecritic.com/forum/464-italy-ports/
San Juan port of call forum:
https://boards.cruisecritic.com/forum/80-san-juan-pr/
St Thomas port of call forum:
https://boards.cruisecritic.com/forum/82-st-thomasst-john/
Recommend you ask/research on the Dominican Republic forum. Lots of great info readily available.
Link:
https://boards.cruisecritic.com/forum/280-dominican-republic/
Personally, I take the NCL transfers every time and have never had an issue over many sailings, neither have any of my friends who use the same service. Just wanted to add a little perspective.