In Dubrovnik, a car would be a handicap. The city is compact and easy to get around.

As for the rest of the Croatian coast, ferry is preferable to road.

Where will you fly out of? Years back, I flew into Trieste, and took the bus down to Opatija (not an immensely exciting journey), worked my way down the coast, stopping at Split, Hvar, Krk and Dubrovnik among others, then took a flight from Dubrovnik up to Zagreb. It was an incredible journey, and all the better from seeing the islands up close.

Slovenia and Croatia are countries I could go back to time and again.

Ferry operator http://www.jadrolinija.hr/