My advise is to concentrate to one Island Group, The Cyclades, The Dodecanese, or Crete (there are more but you referred to these). For a first time traveler in Greece, I would choose the Cyclades, if you come to Greece to see white washed houses and churches with Bougainvillea flowers, blue windows doors and domes, lazy Aegean cats strolling the little Lanes, and donkeys, this is the place. The best islands in my opinion are: Santorini, Folegandros, and Sifnos, and they all are close to each other, and absolutely gorgeous.

I noticed that original post comes from 2011. fcjoseph, maybe you want to do some research to form some ideas, then open a new thread with more specific questions...?

One notice, especially re the campings is that early September can be very different to late September on many islands in terms of numbers of visitors, facilities availiable and weather.