We will be staying in Florence for 4 nights. Is it feasible to do a day trip to Pisa and Lucca in one day? Do we take the train or the bus?
Very easy to do. Note that the train to Lucca does not go through Pisa so you will have to buy tickets for Florence/Lucca, Lucca/Pisa and Pisa/Florence. Or, if you want to see Pisa first, you get the idea. You will be on regional trains so there are no seat selections permitted. You can easily get the tickets when you arrive in Florence.
Get the idea. Thanks