We are doing a Princess Greek Isle cruise in August in lieu of our annual St. Martin vacation. Neither on of us has ever done anything like this and need some help. We are planning to do a few excursions, but really like doing things on our own. So we are curious about car rentals, taxis, buses and non-Princess sponsored tours. We are also interested is c/o beaches. This is our itinerary:

Venice, Italy
Dubrovnik, Croatia
Corfu, Greece
Olympia, Greece
Athens, Greece
Mykonos, Greece
Kusadasi, Turkey
Santorini, Greece
Naples, Italy
Rome, Italy

Any input would be greatly appreciated.