There is a good road network in Crete, particularly along the north coast (E75) between the main towns (Chania, Heraklion, Rethymno and Elounda). And there are main roads towards the south and between the main mountain ranges. Just remember that you drive on the left in Greece and that roads between smaller settlements can be narrow and windy, particularly in the mountains. If you are worried, it is best to avoid driving at night on country roads. Look out for the goats. They have right of way.
For all questions relating to insurance and driving licenses, make sure you get advice before arriving in Greece. Your car rental company will be able to advise you.