Consider purchasing a Eurail Italy Pass before your trip for ease of transportation. Car rentals are also an option for exploring more rural areas. Train travel is generally affordable and ranges from 1-5 hours depending on your destination. Expect to spend around €50-150 for transportation overall.
Consider spending an extra day in Florence to take a day trip to see the Leaning Tower of Pisa. If you're a wine lover, add a wine-tasting excursion in Tuscany. Alternatively, if you're short on time, skip Siena and head straight to Venice from Florence.