itinerary direction

I think a lot of people here will say to do it the other way around: fly into Venice (great place to recover from jetlag and not a great place to fly out of), then Dolomites, then Florence, then La Spezia, then Rome and fly out of Rome (has flights that are not so darn early in the morning).

I agree with earlier poster, fly into Venice and out of Rome.
With that itinerary you need two weeks. Venice three days, Florence 4 days, Rome 5 days.

I agree with the others that reversing the itinerary would be ideal, since early morning flights our of Venice are logistically problematic. Without knowing exactly what you have planned for the Dolomites or CT, I'd recommend spending 3 -4 nights in each of the cities and 2-3 nights each in the Dolomites and CT.

The reason I was going that way is I wanted to end on a relaxing vacation because my husband hates cities but my young adult kids want to see the historical spots and museums.

Welcome to the forum!
Is this your first trip to Italy?
How many NIGHTS do you have on the ground?

It is always easier to fly IN to Venice, out of Rome- although flying out of Venice is difficult it is not impossible. If your departure flight is 11 am or later it is doable. It may require additional transportation expense or not- just depends. You will need to figure out how you will get to the airport.

The problem I see with your itinerary is that you will have to stay night before departure either in Venice or at the airport which is sort of a waste of a night. You can’t drive from Dolomites, drop off car and make a departure flight easily- very risky!

Rome is a bit chaotic and intense so starting a first visit to Italy there would not be my choice. Have been to Rome several times and love it but would not advise first timers to start there.

Why La Spezia? As a base for CT?

If you let us know what time of year this is and how many nights you have we can provide more specific advice.
You may not necessarily need a car for Dolomites either.

Agree with above- you need a minimum of 2 weeks for this itinerary- I would actually want a bit more- you have 5 locations- minimum of 3 nights in each means more than 2 weeks needed.

My husband and I went to Italy 30 years ago, kids have not been, Probably only 7-10 days first week of June. I wanted to go to CT but can cut that if needed. I don’t want to spend that long in Florence unless as a base.

Oh!
7 days. 2 locations
10 days 3 locations

Count NIGHTs not days gives you a better picture

A 2 night stay is really only 1 full day in a location
Each location change eats up at least half a day
You arrival day is jet lag day

Probably only 7-10 days first week of June.

With 10 nights, more than 3 locations is really rushing 'to get to the next place'.

What do you want to see/do at each stop? That will help guide you as to how much time you need at each stop and how many you can fit into to your time

Check out the 'Itinerary" for this tour-- https://www.ricksteves.com/tours/italy/venice-florence-rome -- to get an idea of what you can do. As you will not have a dedicated bus to take you door to door, you will not be able to do as much in the time frame shown.

Perfect night allocation:
Rome 4 nights
Florence 3 nights
Venice 3 nights
Dolomites 3 nights (minimum)
You can take a night off from any, but it will be a rushed visit, because, as Christine said, 2 nights is really just 1 full day at a place. Transfer days are not really touring days. Don't stay one nighters anywhere. One nighters are a waste of time.
Departing from Venice may be an issue since the airport is far from the city center in the middle of the lagoon, that is why most people prefer to do the opposite itinerary, however if you are coming back from the Dolomites, you will simply drop the car at the airport and spend the night at an airport hotel the night before your flight.