to greece or not to greece

There is no airport in Amalfi to fly to JTR. The closest is NAP which has non stops in summer to JTR with Volotea but I doubt every day of the week. Assuming you can find a flight on 8/20, and another back from JTR to FCO on 8/25, you will be able to enjoy Santorini for 4 days: August 21, 22, 23, 24, as August 20 and 25 will be wasted on travel. Four full days in Santorini are adequate. However unless you have visited everything in Italy already during previous trips, there are lots of nice places you could see that are much closer and easier to reach than Santorini. That is a choice only you can make.

As I'm fond of saying: Greece is not as close as it looks on the map.

We are going to be in Italy by train and have decided to add a few days in Greece. The flight from Naples is almost 3 hours and very cheap but we'll see Greece for two days!

If you we're staying in say, Sorrento, and wanted to move on to a place in the Plaka, near Syntagma Square,... the door-to-door travel time with that 3-hour flight would be at least 8 hours.

Once you're leaving Pescara with a rental car, why not take your time getting to Positano by way of the Foggia region? Maybe see Paestum as well? Then drop the car off in Salerno, using public transportation through Amalfi, on to Naples, and the two-hour Frecciarossa to Rome.

Three or four days on Santorini is adequate, but I would still prefer to focus on more of Italy rather than flying to Greece for that short stay. Between Pescara and Amalfi, you could add a stop on the Gargano Peninsula. See the route of Rick's South Italy Tour for more ideas.

I would stay in Italy for those 5 days. Take your pick, go North or go South. I'd probably go North.

I would go to Greece on a different trip so you can take your time visiting Athens, Santorini & other Greek Islands.

South of the Amalfi Coast is the city of Paestum, an ancient Greek-founded seaport (now has a beach) with three beautiful Greek temples and the excavations of the ancient city (first Greek and then Roman). The area around Naples has some interesting sites with Greek or other ancient connections as well - Cumae, the sacred site of the Sybli, according to legend founded by Aeneas after his escape from Troy.