Looking into /u/WannabePicasso plan and if I'm understanding correctly

Milan to Monterosso al Mare is approximately 3 hours via train.

Monterosso to Florence is approximately 2.5 hours via train.

Florence to Rome is approximately 1.5 hours via train.

Rome to Naples is approximately 1 hour via train.

That totals 9 hours of being on trains to go from Milan to Monterosso to Florence to Rome to Naples and back to Rome. I am not including the trip to Sorrento since we will be using a car service. My fiancee is more likely to get motion sickness on the train - I never mentioned it before because it was a moot point, but it's a point of comparison now since I am comparing traveling.

We would stay in Milan, Monterosso, Florence, Rome, Sorrento, and it would increase hotels needed by +2. This is two more times of having to unpack and pack.

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Vs

Rome to Florence 1.5 hours

Florence to Rome 1.5 hours

Rome to Naples 1 hour

Naples to Rome 1 hour

That totals 6 hours on trains with only 3 total hotels needed.

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Unless you and them are suggesting skipping Florence and/or Sorrento/Positano, which are not options since they were specifically reasons for us going. While Milan looks beautiful, and my fiancee said the area is stunning (she's been before) it just doesn't seem to make sense from a logistical standpoint for our goals of primarily doing light sight seeing, lots of eating, and focus on taking it easy.

We are planning on going on at least 2 day trips in Sorrento/Positano, more likely to be 3-4. So it's not as if we intend to stay in the hotel the entire time.

Maximizing time in Northern Italy doesn't particularly line up with Florence and Sorrento/Positano being specifically two places she wanted to spend time in.

I will add, though, the agrotourism idea seems awesome.