I think your number of days in each place looks fine on its surface, but have you considered the time (not to mention expense) of getting from place to place? Paris to Venice is probably simple, but from Venice to Santorini, have you considered the trek (unless you have found a direct flight--which I am not optimistic about in May but I could be wrong.)?
I understand you have likely selected these dream destinations, but you may want to find more geographically simple destinations. I think maybe swap out Santorini for another place in France or Italy (or Croatia would be convenient to Venice). All could give you what you are seeking from Santorini.

You could spend the entire two weeks in France, Italy or Greece... I hope you are planning to go back and re-visit these countries! It sounds like you want to get a little taste for each country, which is fine, but it would probably make your trip easier if you just split your time between France and Italy. Have you thought about Rome? While Venice is certainly beautiful and unique, we personally thought two full days there was enough. If I were you I would either do Paris-Rome-Santorini OR Paris/somewhere else in France-Venice-Rome OR Paris-Venice-Florence/Tuscany-Rome. But, it all depends on your interests. Also, consider how you are going to get from one place to the next and the cost of doing so (ie: it may be cheaper to fly Rome-Santorini vs. Venice-Santorini, you may have a long layover in Athens on the way to Santorini, etc...) I would start looking up train schedules and flights before I really get set on my itinerary.

Also, since you mentioned you like beaches, consider the Amalfi coast or southern France instead of Santorini, which is more difficult to get to.

I think your trip looks absolutely beautiful. Unconventional, but beautiful. When you get to the nitty gritty of logistics, you might find that flying to Greece first and leaving from Paris last is the most efficient. Perhaps when you look at the logistics, you'll end up feeling Santorini is too far -- but then I would suggest the Croatian coast. Malta and Crete will be just as hard to get to and -- guess what? So would the Amalfi Coast.

But I hope you can make your wish list work.

There is a contingent on message boards (including this one) that is waging an ideological war against AirBnB for a whole variety of selfish reasons not worth going into. Many people have used them successfully, but the key to using any rental website is tracking down reviews for rental apartments.

I highly recommend that you post on several message boards, not just one, to get a variety of reactions to your plans. Frommer's has a message board specifically for multi-country trips, and for details like how to get from Santorini to Venice, Tripadvisor's board for Greece (as well as Frommer's) can provide accurate details. Fodor's also has some Greek and Italian residents posting, so that can add to the mix.

But because you want to do something unusual that most people haven't done, you'll automatically get a lot of discouragement. Most travelers do not spend 5 nights in Paris and 4 nights in Venice and 3 nights in Santorini -- but you will be told that you are not spending enough time in each because you want to go to 3 countries, not just one. Had you said that you wanted to spend 4 nights in Paris, 3 in Nice and 3 in the Dordogne -- all in France -- you would have been given applause.

Before you give up on what you want to see, ask on other message boards. Who knows what' they'll say? Maybe in the end you'll want a more geographically confined trip, but you're not leaving next week, so you have time to gather lots of info.

http://www.frommers.com/community/forum.cfm/europe/general-multi-country

I have a European friend who rents her vacation condo using AirBnB and chose it over other agencies like VRBO. Her renters are all Europeans and repeat visitors.As an owner of a vacation property, she is very pleased with AirBnB.

I don't think message boards are what you need--they don't schedule the flights and ferries. You simply need to plug those flights and your specific dates into a search engine like skyscanner. I am all for unusual itineraries, but not when they eat up loads of time and money.

For your interests, those destinations look like a good fit (though I've never been to Santorini). The amounts of time in each place seem reasonable, though it really depends on how much time you want to spend on each of your interests. And of course, you could spend months in each of the destinations!

For my travels, I try to limit the number of countries / languages, because I really like to be able to speak at least a little of the country's language, and I have a hard time switching language on a trip. Obviously, not a deal breaker, but maybe something to think about.

Would other destinations be better? I'm not a beach person, so can't advise you on that. Paris and Venice are fabulous, as are many European cities, for art, history and culture. Venice isn't the greatest city for good food, but hard to beat, IMHO, for beauty.

Most efficient method of transport would be by plane, one of the low-cost carriers. Yes, your three locations are a ways apart, but probably won't take much more time via plane than it would take to get from Venice to Rome, for example.

We prefer to stay in hotels and B&Bs, so can't offer any advice re AirBnB.

I have used vrbo.com to rent apartments worldwide for over a decade with great success. Some require 7 day rentals in peak season but many will rent for as few as 3 days.
Ann Marie

As far as I know, there are no non-stop flights between Venice and Santorini on Aegean or Olympic. You have to connect through Athens, which will eat up a lot of your time.

You might be better off going to Croatia ( Dubrovnik and/or Split) which has beautiful beaches/scenery and easier connections from Venice.

davinhci, I have used vrbo with very positive results. As for flights get on the computer do some research. Kayak for example for flights, you may have to fly into Athens then connect into Santorini airport. Even check other big cities in that area they may offer flights. Good Luck, have a great trip.

Thanks, every one for your input. After much thought with my wife, we will skip Greece for next time and focus on France and Italy. Which leads me to my next topic (maybe I should start another post?). Which cities are good to visit given our interests above? We know we would like start in Paris and end in Venice. We are thinking of going to Versailles, Nice, Monoco. Any other destination in Italy? We talked to people who went to Rome and it was not favorable. For example, it feels like Vegas and too tourist-sy. What do you think?

I have never ever ever heard anyone describe Rome as feeling like Vegas. (Combined with the touristy comment, maybe they were talking about Venice?)

You might want to connect the dots between Paris and Venice with Torino, Lake Como, or Liguria.

Rome will be full of toursists-just like Paris and any other major European city. It by no means has a "Vegas" feel to it! We really loved Rome, there is SO much to see and do. I would not skip it if you are going all the way to Italy. I would even allocate more time in Rome than Venice (3 days in Rome and 2 days in Venice). Some other detsinations in Italy to consider: Cinque Terre (five small quaint beach towns connected by trains and a hiking trail)and Florence with a daytrip or two to the surrounding countryside. Both of those destinations are between Venice and Rome.

Wow, definitely would not describe Rome that way. JMO, but beaches on the Riv don't do much for me. I'd not try to hit a beach in late May in Europe. I'd stick with Paris, Venice and Rome, renting apartments for 4-5 nights each in Paris and Rome. Save the beach visit for a true beach vacation like the Greek isles at a later date. Likely less expensive to fly home from Rome than Venice so fly into Paris and out of Rome.
Ann Marie

You can sure skip Monaco. As others have said, too long in Venice.
Greece is just a bridge too far, as you have decided already. Good.
I am not a big fan or Rome, but it is indeed on the "big" list--and NOThING like Las Vegas, for heavens' sake. What are they thinkin'!!
Florence is wonderful (to me).
Are you flying open jaw? Could do 6-7 days in Paris, 2 in Venice and the rest in Rome--or split between Florence and Rome.

Rome is my favorite city anywhere. I've never heard or thought it was anything like Vegas (and yes, I've been).
If you are interested in culture, art, good food...all wrapped up in 2000 years history, then Rome is the place for you!
Definitely reconsider.

Thanks, all. I will be sure to set my friend straight about their comment on Rome being like Las Vegas. Lets pretend that comment never took place. =)