Greece and the Amalfi Coast

First I'm wondering how you plan to get from Santorini to Venice. Second, it would be helpful to know how long your trip is. In the meantime, a few comments - Venice is far from Naples. You will use up the better part of a day traveling there. Sorrento is lovely, a good base to visit Capri, Positano, Pompeii, Naples, because it is well-connected by bus and train (the local Circumvesuviani). Sorrento is a long way from Milan. Probably you will use up most of a day getting there too. For trains in Italy, use the Trenitalia website to get a good idea of travel routes and times. It won't show the Circumvesuviana, however. The towns have to have the Italian names, even on the English site.

Names to search on trenitalia.com: Venezia Santa Lucia, Napoli Centrale, Milano Centrale. These cities all have multiple train stations, so you'll need to choose the correct station as named above. The Circumvesuviana runs every half hour to Pompei Scavi and to Sorrento. Bus to the Amalfi Coast also runs about every half hour. You might consider flying from Naples to Milano or from Venice to Naples, or both.

We will also be traveling from Venice to Naples, but in late may. I found an overnighter that leaves 1930 and 0600 the next day. It will be our first sleeper and hope we do get to sleep. Haven't booked it yet, but understand we should do a reservation. Will we have any difficulty using our select saver pass and does an overnighter use up 2 days?

It would be helpful if you could indicate a time frame, short of that information, this would be very tight in two weeks. The Greek portion itself is a good week, fifure arrival in Athens, a night there to adjust plus another night to see the sights, ferry to Paros, two nights there at the least, ferry to Santorini, two nights there. The Islands just cannot be done in one night each due to ferry schedules. To get to Venice will require flying or a two day journey by bus, ferry, and train. I would consider flying back to Athens, then catching a flight to Venice or someplace in Italy depending on availability. You will still chew up an entire day in travel. A couple nights in Venice, then a fast train to Naples. Your sequence is a bit confusing, I would just consider basing yourself in Sorrento then visit Naples, Pompeii, Capri, and Positano from there. To accomplish all of that is 3 to 4 nights. If flying out of Milan, you will need a night there, if you plan on seeing sights, then probably two nights. Depending on what flights are available from Greece to Italy (say Rome is easier to get to than Venice) you could flip Venice and the Amalfi, heading to Sorrento first, then to Venice, then to Milan.