The above is a great idea, especially if you consider the additional amazing sites and sights on the Peloponnese (e.g. Olympia, Messini, medieval castles such as Methoni, Coroni and Monemvassia, etc.). Of course, after Athens one could visit Crete as an alternative to the Peloponnese, ot the Northwest of continental Greece Meteora, then over the mountain to Hepirus and, why not, a short ho by ferry to Corfu before going back to Athens.