Comments on our Trip Plan

It looks like you have done lots of research. Just a few comments. AC Rouge Premium is a pretty good way to go. I call it faux business class. Good food and drinks, nice comfy seats but they only have minimal recline so sleep is still hard to get.
Day 5 and 6. the Walking tour troubles me a bit. The Acropolis opens around 8am with a ceremony and very few people around, Once one gets in to the site there will be a couple hundred people enjoying the almost empty Acropolis. By 9:30 thousands of people arrive on tour buses and it gets uncomfortably crowded. From the start time of your walking tour I suspect you will be in the hoard all arriving at the same time. I am not going to suggest you not do the tour those guides know their stuff. What I am going to suggest is on your first day get up to the Acropolis at opening and explore the site. Experience the Acropolis without crowds. When the crowds arrive you can leave and perhaps hike up Philoppas hill for wonderful views of the Acropolis or head down into Plaka for some of the other gated sites. By the way the Central market is an easy walk from the Plaka/ Monestraki area. It is well worth the visit. By the afternoon it will be hot so thats a good time to visit museums. The Acropolis museum is in the central area and takes about an hour or two to do. The National Archeological Museum is in another part of the city about a 30 minute walk as I recall. It takes hours to visit. With such a short visit the Acropolis museum is probably your best bet.
Meteora. That sunset tour is a good idea. During the day the whole area is full of tour buses. At sunset you will have unobstructed views perfect for picture taking. We didn't take the organized tour just did the drive around the monasteries and had the place to ourselves. Good call staying in Kastraki. It is at the foot of the mountains and is close by so you can get an early start.
Next morning get to your first Monastery and get your visit in before the tour buses arrive. The one Monastery we got into had 30 tour buses in the parking lot. We simply couldn't move so that is a good time to drive back to Athens.
Santorini. Make sure that there is parking at your hotel property. It is very tight in Oia and parking can be difficult to find unless you have a dedicated spot reserved for you.
Beaches would be Kamari and Perissia. I prefer Perissia but neither of them are particularly good beaches. No sand just volcanic pumice. Another option when you visit Akroteri would be Red beach. It is an amazing site. I think there is still danger of rocks falling from the cliffs above but last September the parking lot at Red beach was full of cars.

While no longer a winery the Wine Museum Koutsogiannopoulos is a very good experience. It is in the wine tunnels 10 feet below ground and about 300 meters long with stations on the way describing life and history of the winery and Santorini. They used somewhat primitive manikins at the stations which was a bit distracting but other than that this is an excellent tour.
It was unbelievably inexpensive and at the end there is a wine tasting. We tasted 5 wines then my wife asked about a specific wine and they opened an extra bottle and gave us a taste of a 6th wine.
And now for the return to Athens. Four hours is lots of time to make the connection so flying back to Athens the morning of your return flight is probably going to work out fine.
However, bad weather, strikes, mechanical problems can happen. We were on a flight to Athens that got delayed 4 hours. There were Brits, French, South Africans and Australians all missed their connecting flights back home.

I would recommend you fly back the evening of your return flight and stay at a hotel near the airport. Sofital and Peris are both good options.
Santorini http://www.flickr.com/photos/stanbr54/sets/72157632154800782/
Athens http://www.flickr.com/photos/stanbr54/sets/72157632121475515/

Great comments thanks a lot!

• I especially like the idea of going up to the Acropolis for opening one day, in addition to our guided tour.
• in Oia, our hotel does not have dedicated parking. Our instructions are to park in a free lot next to the bus depot. I've looked at it on Google Maps Street View and it doesn't seem to be overly full, plus there is an overflow lot across the street.
• I was going to add to the last point that we're only going in May which I thought would be shoulder season, but perhaps that's a good question: is mid-late May in Oia busy and crowded or is it truly shoulder season?
• I'm afraid the last day flight from Santorini is already booked and non-negotiable. Plus we have trip interruption insurance so the "worst" thing that could happen is we get a free extra day in Athens.

Thanks for taking the time to comment. We may have more questions as we get closer.

Amazing pictures too, by the way. What time of year did you go?

Ok as I said the chances are very good that nothing will go wrong with your flight back to Athens.

Good on you for checking with the hotel about where to park.

My photos are a compilation of several trips. For the most part taken late may and early June but there are a few from September last year. Oia should be calm and peaceful until the tour buses arrive. The crowds will linger until after sunset. If you are lucky you may be there when only one cruise ship is in port. The more ships the more crowded it gets even in May.

We did the Acropolis tour late afternoon, 4:30ish. Crowds were thinning out and it was quite pleasant.

I agree with the comment about parking in Oia. That could be a hassle. Do you really need a car? We stayed in Oia mostly walked. And hired a taxi when needed.

Completely disagree with Red Beach. Very dangerous. Black beach is great. Overall, Santorini is not really a great beach type island.

For sunset cruise, we booked with Capt Ted's Santorini Sailing. Amazing experience. Great crew.

Enjoy.

Everything went pretty much according to plan and we loved our time in Greece.

Top recommendations: Hydra in general; Xeri Elia Douskos restaurant in Hydra; Athens Walking Tours; Swift Avanti car rental; Doupiani House in Meteora; Visit Meteora Sunset Tour; Hotel Aethrio in Oia; Candouni restaurant in Oia.

Regarding The National Archaeological Museum and/or Acropolis Museum, Both museums are wonder and take a while to go through. The New Acropolis Museum is the one you are probably referring to. That will take you 3 hours to see. The Archaeological will take you 2 hours. Don't miss them.

Watch your valuables, pickpockets are terrible in Athens. For men, get a money belt and women a pack safe purse.