Greece itinerary for 10 days

We are a couple from Canada 32 M and 30 F and planning to visit Greece for the first time in Early or Mid September this year. We will do Greece and Montenegro for 18 days of which 8 days will be in Montenegro and 10 in Greece.

So far we have decided to do Athens for 4 days, excursion to Delphi and meteora(not 100% sure) for 2 days and 4 days on 2 islands - picked Santorini(obvio) and Milos(looks lovely).

Does this look good or any other suggestions? I am not too keen on Santorini but my wife is hell bent on going there for Instagram mostly I believe 😛.

Any Greeks or frequent visitors who can guide me as to how to navigate between those places in the best possible way? Rent a car or Uber or any other way? And ferries for those islands?

Also is early or mid September okay for this?