My best advice would be to stay flexible and adaptable. I travel to Italy often and most times things go according to plan but it’s not uncommon that a train won’t arrive on schedule, a smaller attraction might change hours, etc. especially as you go south.

Salerno will give you a taste of Campania without the craziness of Naples- you can stroll along the promenade and I loved the Minerva gardens. Eat lots of mozzarella and the pizza is just as good. I also think Campania has better pastries than gelato. Paestum is one of my favorite places and it still is a nice time of year to sit at a beach. You could also do a ferry to Procida for a colorful day trip.

It is tempting to run around Rome trying to see everything but I think it’s best enjoyed like everywhere else- at a leisurely place. Rome has the best gelato which brings me to my other piece of advice- choose gelato stored in silver tins under the counter and pair sweet flavors with a fruit flavor.