Wow....all that with a child. ^ My parents traveled a lot with me, too, when I was a kid .... but now that I'm approaching 50, I'd never have the nerves to handle that.
We were in Florence this past fall. I'm not sure the exact dates, but we were told that the Westin Excelsior was closing for renovations this winter/spring and would re-open as a St. Regis afterwards.
We stayed at the Grand Hotel .... just across the street from the Westin, and both are excellently located for sightseeing in that city.
It's been several years since I have stayed in the other cities, and will let someone else with more recent experiences make recommendations there.