Need help with itinerary

If you would clarify some points, people can give better help.
Do the 10 days include the international travel, or is it 10 days on the ground? That number sounds like it could be larger. If so, I’d opt for more.
What are your interests?
Florence is not a “big city” in the sense that Rome is, nor is Siena a village. My preference would be for Florence over Siena.
With the amount of time you have, your decision to skip the Cinque Terre is very sensible.
3 nights in Venice will give you, at most, 2.5 days. Keep that in mind when trying to fit in the Dolomites.

Plan on going to IT twice and decide if you’ll visit the north first or the south.

Fly into Rome
4 nights including 1 day trip to Pompeii. I'm pretty set on this part of the plan

Can you clarify if you are set on seeing Rome, or seeing Rome first? Are your flights booked? I would do the reverse order and fly into Venice, then home from Rome.

On a map Dolomites can look close to Venice but keep in mind these are slow curvy mountain roads. I'll be interested in others' opinions but in my mind a day trip to Dolomites from Venice would not be practical or enjoyable unless you are Ok spending the whole day in the car. Enjoy your trip!

10 days on the ground.
Highest priorities are Rome, Pompeii, Venice, and the Dolomites.
I can live without Tuscany this trip.
We won't have a car and plan on traveling by train.
We love nature and ancient places/things. We're not wine people and seeing famous artwork is not a priority. We love libraries, graveyards, catacombs, amazing landscapes, and outdoor cafes.

Oh, and I haven't purchased plane tickets. I'm just beginning to plan. Looking to go early June 2023.

Too much planned in too short of time. You will spend more time traveling between towns than enJOYing the towns. It takes LOTS OF TIME to change towns.
Are your flights booked? For Italy, it's usually best to fly into Venice and out of Rome. So this is what you need to do - even the Rick Steves tour does it this way.

Florence isn't a big city - it is marvelous town. I'd stay there and take a day trip to Siena and San. G with a company called Walk About Florence - check out their website - see their BEST OF TUSCANY tour. Florence has so much to see and do.

Adding Lake Como is going to be tough. You are losing so much time trying to see too much.

For only 10 days, I'd Fly into Venice, out of Rome -- and do 3 days in each town - copy the Rick Steves Venice, Florence, Rome tour and do that Day Trip with Walk About Florence to Tuscany for a day. The trains between Venice to Florence to Rome is VERY EASY.

And if you think CT is touristy - just FYI, so is Siena and San. G and Pompeii.

Italy is to be savored, not rushed. Plan to go back and do the Dolomites, Lake Como another time.

We don't know where you are flying from, but in general (exceptions to every rule, so check), flights out of Venice depart at an ungodly hour, and it's a slog to the airport, so that is why people suggest flying into Venice and out of Rome.
The easy solution is to skip Tuscany--you pretty clearly state your priorities. With ten days, I would do no more than three stops. Keep in mind that the Pompeii day trip is a full day. Because of travel time, something is going to get short shrift. Rome-Tuscany (whether Florence or Siena)-Venice would be more efficient, but there is no rule you must see the big three on your first (or fifth) visit to Italy.

I can't advise on Dolomites transport, so focus on that because Rome to Venice is just a train ride, so making those logistics efficient is your only challenge.
I may have missed what month the trip will take place--Dolomites have seasonal aspects so check into that also.

I'm thinking 3 nights. I hear you can do Venice in 2 days, but a day
trip to the Dolomites is an absolute MUST. Any advice on how to do the
Dolomites from Venice is greatly appreciated!!

That's a really long train ride and a long car ride for a day trip. (although you indicate all train travel)
If the area is a must then stay 2 nights.

Pompeii is a very long day trip from Rome- you will spend a lot of time just getting to and from.
Consider Ostia Antica as an alternative

Or add more nights to your trip. Can you fly IN to Venice, OUT of Naples?

As others have said, fly into Venice and out of Rome. You will be jetlagged when you arrive, and Venice is quieter to relax and get accustomed to Italy. Also, the flights out of Venice are very early in the AM, and transportation at that time can be expensive.
Flying out of Rome is easy, you get a taxi, at a set price, and it brings you right to the airport. No worries.
You could stay in either Florence or Siena, it is a short bus ride between the two. Watch some videos on them to see which town you would prefer.

10 days on the ground.
Highest priorities are Rome, Pompeii, Venice, and the Dolomites.

That is a lot of ground to cover in your short time.

I would liken it to wearing a shoe that is too small. You can squeeze your foot in but by the end of the day you will wish you hadn't.

We found a day trip is not very doable from Venice to Dolomites. My one son REALLY wanted to go to the Dolomites so I spent some time investigating. You can get there by bus but the return is only a few hours later. You can rent a car but unless you go to the airport the rental car places close by 5. The only other option is to go on a tour bus and that was going to be too expensive for a group. So we didn’t go.

And found more than enough to amuse ourselves in Venice.

Some good points above!!!

I'll agree with flying into Venice and out of Rome (or, better yet, Naples) for all the reasons previously mentioned.

IMHO, the Dolomites is too far from Venice for a quality day trip, no matter what tour companies tout for their excursions. If you want to prioritize the Dolomites, then skip something else and give it more time. What I'm also struggling with is that, between the Dolomites and Pompeii, you are trying to cover a LOT of distance in 10 days so something needs to go; I'll personally choose the Dolomites. Do a 2nd trip in the future which focuses on Northern Italy.

The additional risk of of any day trip is Mother Nature cooperating. She doesn't always comply, and the Dolomites in rain isn't probably doesn't match your vision of that trip.

No, Florence is not a "big city"; the historic center - where you'd be focusing your time - is compact enough that we didn't use public transit even once. If "touristy" means being around a lot of other visitors, you're not going to find Siena or San Gimignano or Pompeii much different, crowd-wise, than Florence or Rome so best to adjust that expectation. :O) Yes, Florence is heavy on museums, which you say are not high on your list yet I see that you recently explored quite a lot of those in Paris? If you enjoyed those, you'll enjoy Florence. It's also a good base for day trips, and offers a lot of indoor attractions should you run into a wet day.

Will there be enough in Siena to keep us happy?

Only you can answer that question. Read up on what it has to offer.

We love nature and ancient places/things. We're not wine people and
seeing famous artwork is not a priority. We love libraries,
graveyards, catacombs, amazing landscapes, and outdoor cafes.

If the only catacombs you've seen were in Paris, then you'll find Rome's a very different animal! The Capuchin Crypt aside (which is not considered a catacomb nor is it particularly old), you won't see any bones but the histories and customs of the 2nd-4th century subterranean burials are very interesting so do at least one of them! Landscapes and ancient places? Take a long walk on the Via Appia Antica. Depending on how far out you go, you'll experience views of the countryside outside of urban Rome, pass by the ruins of funeral monuments (burials were not allowed inside the city walls), an emperor's private circus, 2 catacombs which can be visited (tours mandatory but no prior reservations needed), and some other good stuff.

https://www.parcoappiaantica.it

Other cemeteries: three of mention are Cimitero delle Porte Sante in Florence (connected to San Miniato church, which is a must-see in my book and offers a great view over the city); Cimitero Acattolico (Non-Catholic Cemetery) in Rome; and (very large) Verano Monumental Cemetery, also in Rome, for architecture/sculptures.

Pompeii: I don't personally recommend it as a day trip from Rome but if you MUST do it, don't book one of the van or bus tours from Rome. Those spend WAY too much time on the road - at least 3 hours each way - for the scant two hours they usually spend at the scavi. Do it on your own by fast train to Naples (abt. 70 minutes) + cheap commuter train from there to the site (abt. 40 minutes). Posters can help with more detailed instructions how to do that should you need them. Doing it on your own will allow you more time to spend on what is a VAST and complex excavation.

3 nights is only 2 full days and one 1/2 jet-lagged day in Venice. Ditch the day trip and spend one day exploring the old city, and another exploring a few of the islands (Burano, Torcello, etc.)

Okay, sounds like I'm trying to do too much too far apart. So what do you think of this? Still covering a lot, but maybe a little more doable?
Fly into Venice
2 nights - no Dolomites (It was my teenage daughter's wish to see the Alps. She'll get over it. She's young.)
Train to Florence
3 nights- with a day trip via train or tour to somewhere as yet to be determined.
Train to Rome
4 nights - with day trip to Pompeii via train to Naples
Or should we do 3 nights in Rome and 2 in Naples?
Leave from Rome.

Do you arrive in Venice late morning? If so, follow the people on day one so you don’t miss the main attractions and on day two get lost. My favorite Venice attraction is taking a vaporetto from one end of the Grand Canal to the other i.e., the train station and San Marco Square (or even further than San Marco depending on where you are sleeping). Do this at twilight so you don’t see the decay on the exterior of the venetian palaces that line its canal; the experience will take you back in time as your mental walls float away.
You need three nights to see Florence and that does not include day trips. It’s normal to plan too much when you first begin mapping an itinerary and you want everyone to be happy, right? The more you move around the harder it is and you miss a lot when you don’t slow down and savor the moments. Florence has it all, great cuisine and this is your museum city.
Buy tickets for the Uffizi Gallery two months out to guarantee a reservation and book first thing in the morning when you have the most energy; expect to spend two hours there. Afterwards, walk over to Accademia to see Michelangelos’s David. It takes 30-minutes to get a good look at David. On day two explore Florence.
Did you want to see Vatican City while in Rome? If so, do not take a day trip. Assume you’ll return (especially your daughter) and if you follow the crowds in Rome, you’ll see the main sights. This way you can enjoy your hotel, neighborhood and eat well instead of spending time getting from one place to another which is incredible boring and not that scenic.

Your revised plan posted 8/29 is good. I would not add Naples as an overnight; too much transit time.
You can take a bus from Florence to SIena...about 90 minutes or so. Unless you really like a "go-go" pace, there is enough to do in your overnight cities...unless you plan to skip the museums and churches.

We did a similar trip. Flew into Venice, stayed 3 nights which gave us arrival day and one full day in Venice (we took a boating lesson) and one full day to visit Murano and Burano. 3 nights in Rome which included two jam packed days seeing as much as we could. Then 3 nights in Naples with the first afternoon at the archeological museum, then a day at Pompeii and a day visiting the temple ruins at Paestum. We flew home from Naples. I could have used another day each in Rome and Naples, but if you really only want to see Pompeii, an afternoon and one full day would cover it.

We will have to go back to see Florence some day. The trip was very busy as described.