Help with Florence Itinerary

right after the holidays.

To which holidays do you refer?

Do you mean the Christmas holidays?
If so, I don't think that would be a good time to be touring wineries, as it will be winter there.
I'm not sure any wineries will be open for visitors at that time of year.

I would suggest leaving the first day very casual. walk around the city, maybe check the central market, check out the Ponte Vecchio bridge then eat and crash for the night. All the stuff that doesn't require a ticket. Then on day 2 I'd start early and hit the big 3, Duomo, Accademia, and Uffizi.. We just did a food tour of "The other side of Florence" (Eating Europe) and we loved it. That could be something for your 4th day.

I think you would definitely profit from reading a good guidebook. Many (all?) of Rick's books offer sample itineraries for stays of varying lengths.

Our first time in Florence we were there for over 2 weeks (which included an 8 day Best of Florence tour) and never got bored, never ran out of things to do.

Your local library probably has Rick's best of Italy or his Florence & Tuscany books. Take a look; it'll help focus you.

And Happy travels.

If you arrive in the city early enough, take a taxi to Piazzale Michelangelo for a spectacular view of the city. As mentioned by others, get a good guide book. Rick’s books are very comprehensive and will teach you how to get tickets for the museums so you don’t waste time purchasing them on site or waiting in looong lines to enter.

If all goes very quickly at the airport (no line at passport control, no checked bags), you'll get to Florence before 1 pm. You will have to check in and drop your luggage, possibly want to have lunch. Sunset's a little before 5 pm. That gives you 2-3 hours of day light, just enough time for a leisurely stroll to admire the building exteriors (Duomo, doors of the Baptestry, The Uffizi statues, the statues in Piazza della Signoria, the Ponte Vecchio, possibly take a bus to Piazale Michelangelo for the view in the late afternoon light.

Are you on an organized tour for wineries and Sienna? That's an awful lot to cover in a single day. I'd want a full day to enjoy Siena, especially when daylight hours are so short.

I can think of 5 art museums right off the bat, and too many beautiful churches to try to count, each with great works of art - sculptures, paintings, frescoes. Just pick up a guide book at your library or better yet, buy an RS guide and decide what most interests you.

Your arrival 1/2 day is really a throwaway: drop the bags and take a walk before dark and dinner. Most guidebooks have some suggested routes to explore.

With your 2 FULL, unplanned days, do the Accademia and Uffizi on one and the duomo complex (cathedral/baptistry/crypt/museum/bell tower) on the other. Check the details on all to make sure what it on your schedule will be open (Uffizi and Accademia are closed on Mondays).

Just a a few Florentine churches of note: San Miniato (a must-do, IMHO, and that's where you'll get a view), Santa Maria Novella, Santa Croce (Michelangelo is buried here), Santissima Annunziata (on an important piazza +some really good Renaissance frescoes in the entry cloister), Santa Trinita (the frescoes in the Sassetti Chapel are captures of real people in the 16th century), San Marco church/convent museum. Explore your options here and see a few as you have time and/or are nearby.

https://www.visitflorence.com/florence-churches/

Even in winter I'd pre-order tickets for the Uffizi to avoid long ticket lines. You can do that here (and for the Accademia as well) and will have to choose a specific day and time slot:

http://www.b-ticket.com/b-ticket/uffizi/default_eng.aspx

Combo tickets for the Duomo complex can be pre-purchased here. If interested in climbing the dome, you will need to make a prior reservation and can do that on the website:

https://www.museumflorence.com

I'll agree that a "trip around Tuscany to wineries and Siena" is too much for a winter day very short on daylight. Maybe substitute the winery tour with an evening visit to an enoteca in Florence instead as Siena can take up a whole day. Some other posters may have some ideas there, and here are some from a local fan of the grape:

https://thecuriousappetite.com/2019/04/28/where-to-drink-wine-and-enotecas-in-florence-italy/

A walk to the Central Market is a great destination-outside lots of leather booths fof shopping -inside -wonderful choices for meals, drinks, snacks-Try to get tickets to the Academia ( David) for first times in the morning-worth getting up early for. Friends really liked the Double Decker bus tours of the outer areas of the city-restful and a different point of view-usually not recommended but they loved it !