Hi candthomo ---
I agree that it's too much hopping ... I would eliminate at least one island. The easiest would be the Paros-Antiparos combo. It's super-easy to STAY on Antiparos (lower-key, easy walks to beaches) and take the quickie ferry to Paros. You could go over to explore the port town of Parikia, and do the Paros nightlife if that's your thing... then zip back to Antiparos. Then you could do 4 nights on Naxos (the largest island, with most activities), and 4 for Paros-Antiparos ... and the "extra day" will be taken up by the aforementioned "transfer time" ... really it takes fully half a day to switch islands even when you can SEE the next island on horizon.
It would help if you'd share your reasons, for each island, and if you're on a strict budget or not. Here's why:
• IF nightllife is a huge part of why you're going, certainly Mykonos & Santorini have the most clubs. But those 2 islands are also the 2 costliest ones in all of Greece, and can really dent a budget! And already many of the moderate-cost hotels are booked up.
• IF the main motive for staying on Santorini is to experience the famous Caldera View, and you don't necessarily yearn for the club scene or shopping for luxury goods -- you could get the scenery in a €55 daytrip, which runs from either Naxos or Paros.
Finally, because of all that hopping-time, here are some strategies:
• If you haven't yet booked your transatlantic fllight, consider booking one that goes nonstop from N. America- Delta (NYC), American (PHL) or Canada Air (Montreal or Toronto). They'll cost more than airlines that connect in Europe, BUT they are the only ones that arrive between 9 - 10 AM ... the others don't reach ATH until 2 pm onward, and you've lost Day one, immediately. An AM arrival provides many more options. such as --
• Go ASAP to Mykonos. There are many domestic flights (costly but your ambitions require $$). Also you can take a bus, or a $25 taxi to the nearby port of Rafina and perhaps catch an afternoon ferry to Mykonos.
• IF you do Santorini as a day-trip, it makes a return to the mainland simpler, faster, cheaper. Why? A ferry to Piraeus can take 8-9 hours, costs over $70; a flight is $$$ in August. If you're on Paros-Naxos, you can have an entire final afternoon at the beach, then take th Blue Star ferry (€35-38) at 6 or 7 pm arrive Piraeus midnight, and be in your hotel before 1 am.
• BEFORE you book hotels, get your logistics straight. This website - http://www.gtp.gr/RoutesForm.asp - rewards a bit of time, and shows ALL ferries available (just click "8" as month and "Any" for date). This website shows domestic flights for Aegean/Olympic and Ryan air & Air express. http://reservations.airtickets.com/airtickets/com/search.do;jsessionid=A3C7D99EA96EEBE00C1A0A7E57E31253.app6?sid=1&xid=1489414499065
• Finally, when booking hotels, don't try to save a few bucks by the lowest room rate (requires advance NONrefundable deposit) - with the "regular" rate, you pay only duing your stay, and can cancel/change without penalty until 1-2 weeks beforehand.