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.