Here are different aspects about Greece and your possible trip to consider..
Call it what you want but I know you'll gain some insight into many of your Greece Travel considerations!
If you also look at the itineraries listed on the Home page you'll get an idea of how much of Greece its practicable/comfortable to see in how long. You cant see everything can you? IMHO 3 - 4 days in Athens and seven to ten on maybe two islands would be a nice length.
Athens Airport Information: Routes Map to Piraeus and more