If you can, visit Casa Buonarroti, once owned by Michelangelo and left to his nephew, Leonardo Buonarroti. Was converted into a museum by his great-nephew, Michelangelo Buonarroti the Younger. You can see early sculpture including the Battle of the Centaurs as well as an archive of his drawings and letters. You will be astounded by how talented he was even as a boy of 16. There are also a number of commissions for the museum by later artists include Artemisia Gentileschi and Pietro da Cortona.
Grande Museo del Duomo obviously.
Santa Trinità has a fresco cycle by Ghirlandaio. Medici Palace has a chapel frescoed by Benozzo Gozzoli. Monastery of San Marco has each cell frescoed by Fra Angelico. I think there may be/have been a recent Fra Angelico exhibition. Not sure but I remember seeing it advertised. Fra Angelico not really my bag but generally considered very special.
Academia to see David and the slaves. And all the other tourists…!
Laurentian Library
The Uffizi - you can see Simoni Martini, Piero della Francesca, Botticelli, Leonardo and Michelangelo amongst others.
Worth also looking for a Paper Marbling Workshop, you will need to book in advance.
And like Rome, just wander…and enjoy. So beautiful!!