Athens airport to various historical sites, without a car?

We're thinking of doing Greece and Santorini/Crete in a couple of
years. After a recent horrific driving holiday in France, and after
hearing that "drivers in Greece are even more insane than the French,"
we're not terribly keen to do another driving tour. We plan to fly
into Athens, see some stuff in Greece, then hop one of the short-haul
planes from Athens to Santorini and spend several days lying on the
beach and vegetating. The big question is, how feasible is it for us
to use a hotel at Athens airport (or a hotel in Athens city, near the
Acropolis, for that matter) and get out to the following sites
strictly by using public transportation (bus and train)? Thanks in
advance.

1. the ruins of Mycenae

2. Delphi

3. Thermopylae

4. Marathon