Italy trip in early November

Have you purchased tickets? If not, for that itinerary I suggest flying open jaw, either into Rome and departing Venice or vice versa. That way you maximize your time on the ground sightseeing. If this is your first trip, I suggest you spend most of your time in Rome, maybe three or at most four days in Venice and the rest in Rome. I’ve done Pompeii as a day trip and felt it was completely doable. If you do that be sure to eat pizza at Da Michele before you head back to Rome!

...flying open jaw, either into Rome and departing Venice or vice versa...

If you do fly open jaw, it's much better to fly into Venice and back from Rome. Venice is a wonderful place to recover from jet lag. But it is usually difficult to fly from there back to the U.S. due to getting to the airport for early morning flights.

How many nights is eleven days?
Flying multi-city (open jaw) is best. Take advantage of ITs excellent train system: https://www.trenitalia.com/en.html. Names of stations you’ll need to depart from and arrive at are:
Venice - Venezia S. Lucia
Rome – Roma Termini
Naples – Napoli Centrale
To get to Pompeii you’ll need to go to the basement at Napoli Centrale and hop on the Circumvesuviana which is a commuter train that runs between Naples and Sorrento: https://www.sorrentoinsider.com/en/naples-to-sorrento-train-schedule. The name of the Circumvesuviana stop at Napoli Centrale is Napoli Garibaldi. Pompeii is the fourth stop.
I suggest three nights for Venice and four nights for Rome and that includes Vatican City but not Pompeii. To visit Pompeii from Rome you’ll need five nights.

We were in Rome and Pompeii at the beginning of November. We thought that weather was close to perfect though it did feel a little too warm in Pompeii where there is no shade and a lot of rock.

Pompeii is definitely doable from Rome as a day trip, but it wouldn't be my choice. I'd overnight in Sorrento or Naples. However, I can see with just 11 days including flight time why you might not want to change locations. I highly recommend you skip Pompeii for this trip and go to Ostia Antica. I've been to both. I enjoyed both very much. Ostia has a smaller footprint and its close to Rome. In fact, you can get there using metro and a train from Rome and it takes about 45 minutes. Both Pompeii and Ostia are ruins of ancient settlements. Ostia was founded in the 4th century, abandoned and was covered by river silt and is considered Rome's first colony. Ostia is grassier and has some shade. Its quite pretty. There's mosaics and paintings--even a menu in a restaurant.

You should definitely fly in one city and out of the other. A lot of the flights leave Venice very early morning, although it depends some on where you are going. I'm leaving Venice in September for Minneapolis and my flight is at about 11:30am.

I second that Ostia Antica is a good alternative to Pompeii. The first time I went there was in 2002 and we took a picnic lunch. This past December when we were there we found a modern cafeteria/cafe is now on site.

Thanks so much for all the information and suggestions. I have looked at flying open jaw but could not get direct flights which is something I would like to maintain and it was actually more expensive.

There are nonstop flights from FCO (Rome) to VCE (Venice) for less than $100. I would buy a ticket when you purchase your ticket from the US to Europe and back. Sleep in Venice first and Rome last.

I have looked at flying open jaw but could not get direct flights which is something I would like to maintain and it was actually more expensive.

You need to weigh those costs versus all the traveling you're thinking of doing by going from Rome-to-Vence and Rome-to-Pompeii. How much is your time worth because your original plan has you spending A LOT of time, just sitting around watching the views from the window and not enough time enjoying your vacation. There are direct flights from the US into FCO but, the VAST majority of travelers from North America are changing plans in Europe for a shorter hop into Italy.

Both Venice and Pompeii, from Rome are not simple jaunts but, multi-hour legs that would be better spent overnighting at those locations. As was pointed out, you're better off creating an itinerary that is open-jaw, and flying in/out of VCE and arriving/departing out of FCO. Also, great suggestion by Mary Pat, by catching a short commuter flight out of VCE upon landing at FCO, then start your vacation.