Our Tentative Itinerary: Feedback Needed

The Cinque Terre part may be just a daytrip instead of checking into another hotel for one night

Need to cut something. "Two nights" = one day. So you get:

2 days in Rome
2 days in Florence
1 day in "Siena/Tuscany" (how much of "Tuscany" will you actually see?)
Less than a day in Luca and CT.

Start by being honest with yourself. How many FULL days do you have in Italy, not counting the day you arrive or the day you leave?
Looks like maybe 8 or 9? If that's true, I think you pick two places.

No Venice?

I'd fly in to venice, do a couple days there, then do a quickie stop in Florence on the way to Rome. Fly home from Rome. I don't think you don't have time for Seina, CT, or Luca.

Remember: short days in December.

4 nights each in Rome and Florence- 2 nights Siena/Tuscany

If flying in/out of Rome, go to Florence 1st and work your way back to Rome.

Regarding CT , would you go to the Oregon/Washington coast in December?

All that time checking in and out of hotels is wasted time. Aside from the fact that you really have too many stops for the available time, I would not sleep in Florence, Siena and Lucca. They are reasonably close together. Stay in Florence and day-trip to the others. And since the weather may not be appealing, I'd plan the Cinque Terre as another day-trip from Florence, depending on the weather.

While it may not be summer, the December holidays bring lots of tourists. I would drop the CT - it's a very long day trip in summer, when days are long. You will have long evenings. I would spend them in places where there are things to see and do then. Maybe someone else can tell you if much of anything would even be open in the CT then. If it isn't sunny, it probably wouldn't be scenic. If you are going to be in Italy over Xmas and/or New Year, check what sights are open and what the train and bus schedules are.

I would recommend skipping the CT as well, and doing Lucca and Sienna as day trips from Florence. IMHO, the minimum to manage Rome is 4 nights/3 full days, and I'd say the same for Florence, although some of us enjoy what that city has to offer more than others. It depends on your interests?

Your airports of arrival/departure will impact the order of your trip and possibly how many days you need to give certain locations. For instance, if you're flying out of Rome/Fiumicino, you will likely want to spend your last night in the city or near the airport if your flight is very early.