Greece Transportation questions

Fly. I assume to get from Santorini to Corfu you'll need to transfer in Athens. (Or did you mean Crete in your third question?) You need to be careful about that. If you end up with two separate tickets, do you have any protection if the first flight is late or gets canceled, causing you to miss the second flight?

I use Skyscanner for researching intra-European flights. I book each flight on the appropriate airline's website.

I would recommend flying, for each one. You could drive from Corfu to Athens, and you could take a ferry from Athens to Santorini. This would be a much more leisurely trip and you'd experience more of Greece. But if you just want to travel efficiently: fly.

I would also consider sticking to one island group so that you can ferry between islands. There are much better ferry connections within island groups than between. For example, you can go to Santorini and a variety of other Cycladic islands rather than Corfu which realistically requires going to back to Athens and flying.

Corfu and Santorini are far apart. I would fly.

Thank you for your help.

Unless you can stay more than 3 weeks in Greece, that's a lot of places to visit.

If your goal is Athens + islands, as BethFL advised, I would focus on Athens and a group of islands easily linked by ferries in the Cyclades, Ionians or Dodecanese Islands.

If you want to organize your trip by yourself, this kind of project requires a little preparation and research work. Looking for places with available accommodations, how to get from point A to point B, how long it will take, what are the flight options, timetables and ferry possibilities. All without going over your budget.

Check Ryanair. They have a flight that connects Corfu to Santorini in really good prices. Also for Athens to Corfu Check skyexpress.