OK, some random thoughts:
1. When in Rome, just tell yourself that you'll get back again before you die. That way, you'll pace yourself in a way that you don't try to see everything, and you'll enjoy everything you see that much more. Another good pacing tool is to stop for a gelato every two or three blocks as you walk around. You won't gain weight, and you won't regret it.
2. In Rome, the Vatican/St. Peters is of course a must see, along with the Coliseum area (shocking how 'modern' the stadium infrastructure is and the scale of it). I have so-so memories of the forum as I spent most of the time walking around with a child on my shoulders in 97 degree temperatures. Gnocchi, Pizza, Caccio e pepe. Also enjoyed just hanging out by the Spanish steps.
3. Do be vigilant at the train stations. At least when I went, it was sort of like the oklahoma land rush, and a young lady next to us accepted a kind, well-dressed gentleman's offer of help with her luggage, and he promptly absconded with her bags.
4. Most simply love Florence, I was somewhat underwhelmed by it. Obviously the David, Uffizi, Duomo, and Ponte Vecchio are must sees, but most of it just seemed like a city to me. Again, I, rather than others, seem to be the outlier here.
5. If you have wheels and are feeling up for a (long-ish) side trip from Florence, I loved Assisi. There's a peace and quiet about the place, and I never really "got" Giotto until I saw the frescos at the Basilica. Alternatively, another long-ish side trip would be Montalcino to drink brunello.
6. Just went to the Amalfi coast this summer, and stayed at a little place outside Minori. In general, I wouldn't recommend a car, it's just terrifying to drive the coastal road. Also, in summer, it will be very crowded; be prepared. Pick up some colatura d'alici (pressed anchovy oil) somewhere in your travels.
7. There's not much to see/do in Minori but there is an absolutely fantastic little restaurant there called Ristorante Pineta 1903. Another highlight is to hike the path of the lemons from Minori to Maiori - groves built on improbably steep terraced slopes. In Maori, there's a boutique limoncello place called Carlo Massi, right near the end of the path of the lemons. If you want to climb, from Maiori you can head up to Ravello.
8. Liked Amalfi and Positano - great shopping in both, but better in Positano. Sorta cool how each of the churches in these little seaside town have their own little stories of Marian appearances, icons, etc. Got lucky and saw a 'high-end' wedding, complete with drone photography, in Amalfi, though I pitied the bride walking up about 60 steep steps to the door of the church in her full gown. We were scheduled to go to Capri, but bailed, and I don't really regret it as I tend to feel like a captive on a boat.
9. Absolutely LOVED Pompeii. Just amazing in terms of the scale, the preservation, and the sophistication of design. Don't bail early because you're tired.
10. Finally, one of the things I really love about Italy to "be on the lookout for" is how the architecture reflects the political history of the particular place - whether it is the imperial Rome, the physical manifestation of a "city state" atop a hill in Tuscany/Umbria, the 'democratic' square buildings of a commercial republic in Venice, or the defensive outposts along the amalfi coast.
