Although I wasn't thrilled with lodging in Florence, you will need at least two busy days to cover the must sees. Get reservations for the Academia and Uffizi so you don't miss them.
I would spend the fewest nights possible that will give you two good touring days in Florence.
One day and night in Siena works pretty well.
An extra day or two in CT always works. My wife liked relaxing by the water and the kids were never bored feeding their pizza crumbs to the fish, birds and cats, jumping in the water and collecting shells at Monterosso beach. Everyone enjoyed hiking the trail and riding the milk run train through the tunnels and villages.
In CT, we didn't book a hotel. We negotiated for an apartment when we got there. It was October, not sure if you could plan for that in summer.