www.greecetravel.com
This is my favourite online Greek travel source .Well-researched and far more honest than some of the more traditional guides such as Fodors etc.It also has an up-to-date information on the ferry system ( which also has its own website. ) A Rough Guide to Greece is a good book to take with you as is this.
http://www.amazon.com/gp/offer-listi...condition=used
Funnily enough Matt recommends a travel itinerary not dissimilar to the one you are planning.
http://www.fantasytravelofgreece.com...-pleasure.html
My first advice is to book nothing in advance except your hotel in Athens, do the sights as quickly as you can and then leave as Athens is not the greatest city in the world to be a tourist.Keep a close eye on bags and wallets as petty theft is rife.
A hard and fast schedule with all hotels booked in advance is not necessary at the time of year you're travelling ( one of the best.) July and particularly August are the really busy months.
Abandon the idea of a traditional holiday where you move from one recognisable chain hotel to another.
There are plenty of very good quality hotels especially on the bigger islands you're thinking of going to.
But the charm of the Greek islands lies in their simplicity.
Be flexible and find an island you like,stay as long or as short as you like and then simply move on to the next when you fancy a change. You can book a hotel at the next island from the one you are leaving of whatever level of quality and comfort you require.You might even consider local guest-houses and B+Bs of which there are thousands.
All ferries and fast hydrofoils tend to leave from Piraeus every morning.
Pick a group of islands such as the Cyclades or the Dodecanese which are served by inumerable ferries and fast hydrofoils daily.It's much more unusual to get ferries travelling from one group of islands to another.
The four islands you have chosen are a huge distance apart and without checking on airports,flights etc you may well have to double back to Athens to reach all four which means you're going to be spending a lot of time travelling.
Rhodes is a holiday destination all by itself and much favoured by European 18-30s, Santorini is a tourist trap,Mykonos is party central and Zakinthos is nowhere near any of these.
Do your research carefully as all the islands are different. Some,such as Naxos,are green and fertile others are barren and windswept.Some have great sandy beaches,others are rocky.
Travel really light - the Greeks are very informal.You don't have to dress up.You'll need nothing heavier than a light top in case the evenings get windy.Coats ? Never.
And get into a Greek time-frame as soon as you can.
They siesta at lunchtime and eat late in the evening because of the heat. It's not uncommon to see a family sit down to dinner at 9pm or 10pm.
Food is much improved from the old days - lots of fish,grills,salads as well as the usual intermational menu.
Forget about hiring a car. Everyone travels by bus on the Greek islands. They're noisy,busy and great fun but don't expect anyone to wait in a queue. Those little old ladies scuttling towards the door all at once take no prisoners.
Travelling the Greek islands is like no other trip and it's hard to explain the allure and fun of doing it until you've done them.If you take only piece of this advice it would be to be flexible. ( And try to reach Koufonissia ! )