Greece late June 2020

There are a few problems with your plans. First, the ferry from Athens to Santorini is pretty long - about 4 or 5 hours. I love being on ferries 'sailing the Aegean' but even for me that's a long ferry ride. Second, 4 days in Crete is not very long, it's a very large island. Third, if you fly back to Athens and then fly home you are probably doing it on two separate tickets so it can be a pain to coordinate leaving enough time to be 'safe' vs too much time 'wasted'.

So here is a suggestion. Ferry to Naxos and/or Paros (either 4 nights in one of them or 2 + 2). The ferry rides are much shorter and thus more pleasant. Then continue on to Santorini. Then fly from Santorini to Athens and do your Athens time at the end and fly home from there. Crete is lovely but 'deserves' a week or more to even see half of it, save it for a future trip. All the things you mention you want to do can be done in Naxos and Paros. Santorini has a great archaeologic sight and from Paros you can do a day trip to Delos, one of the 'best' archaeological sites.

Also, stating that an ABNB 'makes more sense' than (I assume you mean hotel) doesn't really 'make sense'. What makes sense is figure out where you want to stay, then look at options (booking.com has all kinds of accommodations including hotels, B&Bs, apartments, etc.). Many hotels in Greece are very small (10 rooms or less) family run places, not large chain or 'fancy' hotels. Then choose whatever makes sense. Don't limit yourself to one type when you search.

I'm sure you can hire private tour guides, especially on Santorini, but you should know it's not really necessary. Maybe do tours to the archaeological sites.

I agree with Isabel. 8 days is quite short for the amount of things you want to do, esp. bc travel time between places is long (½ day for each change). Crete is big, and maybe you have only one destination in mind for your visit there, but even with that, it seems that a separate or longer trip would serve you better bc there is so much more to do there than any one place (like Chania or Heraklion).
Look at flights to the islands, and compare prices and timing with that of ferries. I realize that taking a ferry can be an experience in itself, but they do take hours, so you may want to weigh your desire for that experience with the practicality. We ended up taking a ferry from Piraeus to Crete, and then from Crete to Santorini, from Santorini to Naxos, and then from Naxos to Athens (which we did do at the end). But we traveled for a month!
Maybe fly into Athens and transfer to a flight directly to Santorini. Then ferry from Santorini to Naxos, and then either fly or ferry, depending on how it works time-wise, to Athens and end your visit there.

Thank you for your responses, this is extremely helpful. Sounds like we should end our trip in Athens instead of at the beginning of our holiday. We will look into the islands recommended and may consider spending most of our time in Crete. Grateful, D