Month of travel? Crowding is a big issue from May to September, in every mode of transport in that area.
There are pickpockets everywhere in the world. Since we wear "Rick Steves" under-trouser money belts, we don't care much about pickpockets. We did find the Circumvesuviana so fiercely crowded and physically hot that it was an easy decision to take a car service (+- 90 Euros) back to the Naples rail station. But that decision was also driven by the outrageous 15 Euro cab fare from the Sorrento Circumvesuviana station to our hotel, Ambasciatori. It's just barely too far to roll suitcases, but not worth 15 Euros.
A specific problem on the Circumvesuviana is finding a spot to stand (and then supervise) your suitcase(es). Every inch of the car is literally crammed with people. But the price can't be beat, for budget travelers. The only luggage racks are bus-sized little racks over the seats.
The general consensus here is that Pompeii demands two hours. Four hours are needed to really appreciate it. Heat and sun suggest that summer visits should be as early as possible in the morning.
We skipped Vesuvius. It looms over everything, which is the point. But why trudge up a dusty, cinder hill in the beating sun? I've seen Mt. St. Helens and Hawaii's firery volcanoes. I don't need to hump up Vesuvius. It may be relevant to tell you that we've been (daytrip) to Capri twice, and we skipped The Blue Grotto both times. (We have seen a similar grotto in Croatia, which made it easier to save all the time involved in Capri's blue grotto.) OTOH, we bought the three-day, five-site ticket, and went to Pompeii, Herculaneum, and Oplontis on various days out from our five nights in Sorrento. It is absolutely unnecessary for you to see all three of these, I'm just contrasting it with "skipping" Vesuvius and the Blue Grotto. You have your own travel style.
It does bother me when posters suggest that less ambitious visitors see Herculaneum "because you can see all of it in two hours." Both cities are still, MOSTLY buried under modern cities with the same name. As our host Rick writes, Pompeii clearly must have had a Synagogue, which would be a major tourist attraction. But it has not yet been found. Because of the modern city, it is likely to never be found. Herculaneum would be better for physically limited visitors, but it is a 15-minute, downhill, walk from the Circumvesuviana station. And it has no food sold inside. (Re-entry on same day tickets is not allowed at the five ancient sites.)
You may wish to use the search box top center with terms like "Pompeii Sorrento" or "Pompeii Vesuvius", and then click on the Forums filter, and then on the time back you want to consider reports. Your questions come up often here.
Edit: It sounds like bragging, but we paid extra for a view/balcony room at the Ambasciatori, and we saw Vesuvius and the gulf outside our window every day. Yes, it's far away. But it's an iconic view. Very valuable report farther down about the fast ferry from Naples. We were on a similar ferry Sorrento-Capri, and it had hundreds of airline-style seats, in an air conditioned cabin. But no significant view, even from the few, part-open-air decks, which were in the shadow of the bridge deck.
Sorrento is built on a cliffside. The marinas are a substantial distance below the top of the cliff. There are taxis, public busses, and a 2 Euro (?) elevator which goes to a nice part of downtown. But you'll have your bags.
I forgot to mention that Sorrento has only one, tiny sand public beach, between the two marinas. It has an aroma of diesel fuel! The expensive hotels have boardwalk swimming platforms below them, reached by the hotel's interior elevator. Hotel guests only. I don't really mean that as a slam, but it's a fair description.