long stay Italy touring

My wife and I are thinking about heading off to Italy for 2 months or so, April-May, next year. We have a 2 berth Swift Charisma being towed by a Honda CRV. Our plans are to eventually cross over from southern France and plan to tour around the Florence, Rimini, Venice, Milan areas stopping at sites in these areas and using public transport to visit the cities tourist attractions. Can anyone reccommend sites in these areas and any other information you feel would help us along the way. Also we would like to know if the ferry companies have such a thing as an open return as we might not be in such a rush to come back if we are enjoying ourselves. All recommendations and advice would be greatly appreciated.