Itinerary Help Please

Have you considered taking a cruise thru Greek's islands? They are a very easy way to travel and priced very favorable.

I flew from Athens to Paros, then took a ferry to Santorini. From Santorini I flew back to Athens. The ferry is a good way to visit other islands and is very scenic. Both islands are gorgeous and worth the visit. You could do Paros, then ferry to Naxos, then ferry to Santorini, then fly out from there back to Athens.

You could fly to Crete and see Chania and Heraklion for 5 days
Then ferry to Santorini for 3 days (Stay on the Caldera between Fira and Oia)
Then ferry to Paros (3) then to Naxos (5), then either ferry to Athens or fly
Finish in Athens (3)

I like what Arya has suggested.

I would add a few days to Crete, however, since it's so large. But you could do 7 days on Crete, then ferry to Santorini (3 days is more than enough) and then to Naxos (5). That's 15 days.

I never allot more than 2 days for Athens and you should reserve those for your last 2 days since you will need to be close to the airport. That leaves 7 days, hopefully.

For those 7 days I would visit Meteora, Delphi and Nafplio though there are countless other spectacular options on the mainland.