– Any advice on where to go after for around 5 nights? Back to Naxos (we didn’t really move from the town last year unlike in Paros where we rented a car and saw the whole island)? What about Folegandros? Tinos? Milos? We would like somewhere with a nice town to walk around, upmarket, more couple less family, nice bars and things to see during the day bit also nice beaches etc?
To sum up: a lot depends on your own stamina because island hopping means packing and unpacking, getting on and off buses and ferries. Limit your choice of islands to perhaps one or two less than you think you can manage. Maximise transport links to avoid backtracking or port-transferring and since you are traveling high season be aware that you will usually need bookings ahead at most places. It is possible to turn up on an island and not find a place to stay or have to make do with a third-rate option.
The only ferry from Kusadasi to Greece goes to the Greek island of Samos. It’s a great island and certainly worth a few days. From Samos, there are usually direct ferries to Mykonos and Syros. These are very different islands that have a very different vibe – but both appealing in their own way. From Mykonos there will be direct flights to Western Europe (most likely Rome, Paris, Amsterdam, and London) though not every flight flies every day so requires some planning. Santorini would be another ferry ride from Mykonos. And Crete farther still. So you wouldn’t have time to get to either island.
Since airline reservation requests are often made by city-pair (such as "show me flights from Chicago to Düsseldorf"), an airline that can codeshare with another airline for a variety of routes might be able to be listed as indeed offering a Chicago–Düsseldorf flight. The passenger is advised however, that airline no. 1 operates the flight from say Chicago to Amsterdam, and airline no. 2 operates the continuing flight (on a different airplane, sometimes from another terminal) to Düsseldorf. Thus the primary rationale for code sharing is to expand one's service offerings in city-pair terms to increase sales.