Hi! Ambitious travel plans you have!
Having formerly lived in Greece and travelled to all the places you mentioned, I would definitely say you MUST keep Rhodes in the itinerary. It's a beautiful island and Old Town Rhodes is pretty interesting and neat. Faliraki is the area of Rhodes with the parties, although the British meat-head tourists can get a little rowdy. And when I say meat-heads, I mean the blokes skunk drunk arguing Arsenal v. Liverpool v. Chelsea v. Man U.
Anyway, a few things, on Crete, I recommend the eastern end of the island. Agios Nikolaos, Hersonissos, or Malia. Stay there. Rent a car and drive to Chania and the Samaria Gorge for the day. But stay on the eastern end. Nicer. Better beaches.
Athens is not all that exciting. 1 day at the Acropolis and it's "been there, done that".. stay on the islands and enjoy the unique Aegean atmosphere.