Itinerary Suggestions ? Advice Requested for this First Timer

I suggest you go to GoogleMaps to find your Venice hotel. Looks as if you could either take a cab or city bus out to Venice and catch the vaparetto that stops at S. Sylvestro. Your hotel is on a small canal a few blocks farther and off to the right than S. Sylvestro.
You really might want to reconsider trying to do the C/T from Florence on a day trip. If you want to see it, go there from Bologna and spend a night or two.
If you want to see Lucca, you should see the city on your way from La Spezia and the C/T. Then go on into Florence by train.
Many people prefer to drop their Hertz cars in Orvieto across the street from the train station. It's also a very popular hilltown to see. The train into Rome Termini is just over an hour on a local train (no reservations.)
Others familiar with the Amalfi Coast can chime in, as I've not been past Naples.

If you are booking car thru AutoEurope ( highly recommend) they no longer deal with Hertz in Orvieto so you could consider dropping car in Chiusi then train to Rome.
Or if driving to Rome is your choice then others will have to advise where to drop in Rome.

I like to use www.rome2rio.com to see what transportation options are available. If you put in your Rome address and either Termini or where you drop car it will show all your options ( just use this for options, don’t rely on prices)
A cab from Termini would be my choice, unless your lodgings are walking distance from there. Go outside and wait in the official taxi line, don’t be misled by anyone who approaches you in the station offering a taxi- they are not legit.

If you decide to go to Sorrento give it 3 nights. It will take half the day to get there, then 1 day for Pompeii, 1 day for Amalfi coast sites/ touring.

That's true about Hertz in Orvieto. In Chiusi [closed Sunday] they open at 9:30-12:30 [Mon-Fri 3 to 7] and the first train to Rome is at 10:54. Drive to the station and make a left; thy are in the next block.

For this CT day trip you would want to take the train from Firenze Campo di Marte to the village of your choice at 7:28AM, changing trains at La Spezia:

https://oraritreniitalia.com/orari-treno-regionale-21182

There are no ships the 15th and 16th. You will be spending approximately 7 hours on trains and going to and from stations.

IME 2 nights [a single full day] are not sufficient for Sorrento et al. Advise adding to CT, spending 3 nights. Note that it's most pleasant early mornings and evenings.

I also think there's no point to going to the CT on a day trip or to Sorrento for less than 3 nights, and I'd recommend 4 at a minimum. Stay in the CT for 2 nights or more; you won't need the car in the CT, you could go there after Tuscany and drop the car in La Spezia. Then take the train to Rome (there's at least one direct train a day - fastest and easiest).

I also think there's no point to going to the CT on a day trip or to
Sorrento for less than 3 nights,

Voting with Chani here. While I gently disagree with a previous poster that it'll be 7 hours of train time to get to/from the CT (quickest: the 7:28 from Firenze Campo di Martre to La Spezia takes 1 hour and 43 minutes; the one back at 20:03 takes 1 hour and 42 minutes, and trains in between the villages take just minutes apiece), day tripping means spending your day in the middle of the other day trippers, ships or no ships. That region is best visited with an overnight or two so you can enjoy the golden hours when the day trippers are not around.

Given the time it takes to get there and get around, Sorrento/Amalfi Coast needs more than 2 nights/one full day to reasonably explore so I'd scratch that one.

We were not so impressed with Bologna, but loved Ravenna.

You can easily do a day trip from Florence to Siena. You can also do one for Pisa and Lucca. Six days in Tuscany is nice, but six more days after Florence? Consider Umbria: Orvieto, Assisi, Perugia.