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 St. John is part of the U.S. Virgin Islands, U.S. citizens can visit without a passport. There are quite a few bargains on both St. Thomas and St. John right now, so it’s a good choice for travelers on a budget. Snorkelers should not miss visiting Trunk Bay, one of the best snorkeling spots in all of the Caribbean for seeing amazing marine life.