First time trip to Italy what region?

What month?
I would not fly into Milan because of the distance from Sorrento--Rome is much closer.
It helps a lot for you to make a potential plan and then post that for feedback.

Ok good to know! So, we will fly in to Rome and spend a day 1/2 there. Then travel by train to Sorrento. Would like to make this our home for the rest of the time but not opposed to going elsewhere to another airbnb if needed. Where can I get to from Sorrento that’s a must?

https://www.ricksteves.com/europe/italy
Try the search first--there is a ton about this area on the forum!

If you want to stay in Sorrento flying in to Milan makes no sense
Fly in to Naples if you can, otherwise Rome
You need to do a lot more research

Since you are sort of on "square one" with your planning, what I would suggest doing as a starting point for deciding where to go is to look at the itineraries the various group tours offer, so you can sort of "hijack" ideas from those. Then look at on like postings/photos on places like tripadvisor.com to see what appeals to you.

Rick Steves, Tauck Tours, NationalGeographic Tours, various bike tours, etc. could be good starting points to get ideas for independent travel.

We have traveled to Italy three times.........first with Rick Steves (Heart of Italy), then with Tauck (Amalfi Coast), then Venice (SeaCloud), and we do not feel that we have come close to seeing it all. Still yet-to-see, the Lakes and the Southeast section. It is all so beautiful, you really can't go wrong..........you just need to pace yourself and not try to take in too much to quickly. Allow yourself a slow day after landing, then allow yourself a slower day in the middle of your itinerary if you are go-go during most of your time. I think it is best to have at least two-night stays in each location, longer if you can sort of branch out easily in different directions in certain spots.

Hello,
You didn't say what time of year you are going, but keep in mind Pompeii is very hot in summer, with no shade. Just a heads up on that.
You have many options: Go to Pompeii on your way to Sorrento from Rome, or take a day while you are in Sorrento. (that's what we've done)
From Sorrento, you can visit, Capri, Ischia, Amalfi and Amalfi coast, depending on how much further you want to venture.

And, FWIW...Rome is unique and deserves more than a couple of days, so plan to return!

Sorrento only really works for a base for a limited number of places. Mainly, Naples, Amalfi Coast, Pompeii, Capri, maybe Salerno. Much beyond that, you waste a lot of time (an hour or more) just getting from Sorrento to either Naples or Salerno to get to someplace else. Ten Days would be fine to just do the Naples area with maybe a couple days in Rome.