Mykonos, Paros, Naxos, or Syros

Thanks for the advice. How far in advance are the ferry schedules usually released?

At least a month before theyr'e needed, but some sooner than that. Check with www.openseas.gr and www.gtp.gr.

You can be fairly confident that Blue Star Ferries will be running from Santorini to Naxos and Paros in April (enroute to Piraeus), and that Hellenic Seaways FlyingCat 4 will be running the Heraklion-Santorini-Ios-Paros-Mykonos route during that month as well. These are regular services that have more or less the same timetable each year. Getting from Santorini to Syros may involve a ferry change at either Paros, Naxos, or Mykonos.

Should you be completing your travels in the first half of April, Naxos and Paros will be very quiet. Mykonos would be more lively, but beware the week leading up to Easter, as ijuliano mentioned. Syros, IMHO, would be a more interesting stop than the others in early April.

Thank you again for all of the good advice!