Having just skimmed this thread, I have an alternative suggestion for Florence. Take a taxi to the Roman Gate. Ask the driver to point you back to the center. The exact route doesn't matter. You will walk through the artisan district, the tassel shops, chandelier makers, jewelers, fine fabrics, eventually coming to the Arnau to your right about 4 blocks away is the Ponte Vecchio. Do not cross the river, but find your way over to the Ponte V, and walk across, continuing straight up the main street. You will walk in the footsteps of those who came in awe to this city, passing the major monuments (at least within sight) and ending in the square with the Duomo and the Baptistry doors. Even, or especially, non catholics will appreciate the power of the church from admiring this square. This will take from 2-8 hours, depending on how often you stop, how many little shops you enter, ect. Oh, don't forget your camera!
See if you can find a copy of George Oakes "Turn Right at the Fountain" in your public library for wonderful descriptions and walks in Florence. Not much has changed since this published, old as it is.