This itinerary includes some of the major archaeological sites of Greece and a tiny sampler of Greek islands through a day-long cruise. It would be best for those who desire a balance between ancient culture and a bit of sea venturing.
It is by no means a laid-back trip, and it requires extensive travel between different locations so it's recommended for those who prioritize "ancient Greece" above all else. You can modify the trip to be a bit more comfortable by ommiting Olympia and instead spending a night at the island of Hydra, or spend another day in Athens to Sounio and Lavrio. With extra days in Athens, you can visit the Acropolis and its museum, the National Archaeological Musuem (both shoud be on everyone's itinerary), plus the Agora and its Museum, Kerameikos and its Museum, and possibly Sounio or the Museum of Cycladic Art.
It would be best to rent a car on day three to drive to Delphi (and Olympia if you choose so) but I would not recommend driving in Athens. You could choose a hotel in the center of Athens and you can reach the port of Pireus by taxi or metro for your trip to the islands. If you opt for a one-day cruise instead of a hydrofoil, keep in mind that the small cruiships that sail from Faliron (not Pireas) are not what one would consider "luxury" boats. At best, they can be considered glorified ferries with limited ammenities. The one benefit from such a cruise is that they take you to three islands (Hydra, Poros, Aegina) but the time at each port is extremely limited. If you opt to sail by hydrofoil on your own (recommended), don't bother with Aegina or Poros, and opt to spend extra time at the picturesque island of Hydra. You should make reservations ahead of time if you plan to spend the night in Hydra since accommodations are plenty, but the island is very popular.
There are no cars allowed on the entire island of Hydra (save for the municipal refuse truck) so you don't have to worry about it. The only drawback with these trips, is that you would be spending a lot of time in Athens, a place I would not consider a good representative for those who want to experience the beauty of Greece. But Delphi, Olympia, and the Saronic Gulf islands could balance that part with their charm.