Can you see ahead of time what excursions your cruise ship offers ? Good fun planning ahead ! From Livorno, you could take excursions to either Pisa OR Florence, I would be stuck which to choose.
We've been to Naples twice. I would recommend Pompeii because it so huge and breathtaking...........its a large town not just a site. Last time we did Herculaneum............but it is tiny, a 2oth the size of Pompeii and not as well run by any means.......looked at my scrapbook of that cruise where I'd felt that "Beautiful, preserved frescos and mosaics, go to Herculaneuam to complete your tour of Pompeii but not worth a trip of its own. I'd visit Pompeii again in a heartbeat and the bay of Naples itself is stunning.
DH is part Maltese so yay to visiting Malta ! Beautiful ! You may be amused at signs of the British there, red telephone boxes etc.
WE did not regret taking the most expensive detailed excursion to Rome. 10 hours was barely enough. Gelato at the Trevi fountain, Piazze Navona, Spanish steps, the Pantheon, so much time in the Vatican and in St Peters. Castell St Angelo. Amazing.
I have wanted to see Kotor and there are lots of options from Toulon. YOU do make friends easily on a cruise ship and if DH is all touristed out and wants to just relax on board it is fun to go offshore with new friends.
Your trip sounds amazing with my one exception Sit on a sun lounger on deck with it pointed AWAY from that port and you'll be all set ............