Draft Itinerary Greece Islands + Mainland

Logistically, does it make more sense to visit the islands after the
mainland tour, reverse the island circuit, and fly from Santorini or
Naxos (if there is an airport in Naxos) to Paris?

In Greece, it's preferable to visit the mainland after the islands. This is mainly due to the possibility of ferry cancellations due to bad weather, strikes, or breakdowns.

In your plan, it's less problematic if your trip ends in Santorini before going to Paris, since there are direct flights from Santorini to Paris and Santorini has an international airport. However, you'll have more Athens-Paris flight options.
So ending in Athens makes more sense.

Naxos has a small regional airport with only domestic flights to Athens.

...and whether these flights and ferries require early booking
(assuming so for flights)?

No need to book ferries in advance. If you're anxious about booking, just book 2 or 3 days ahead.
Flights are a different story, as they're generally booked before anything else, and Greece is no exception.

It sounds like it might be possible to carry a carry-on backpack piece
of luggage with me.

Yes, you can take a carry-on backpack with you. (try to be discreet if it looks large). You leave your other luggage on the deck provided for this purpose. No one has access to the luggage deck while the ferry is sailing.

Is there a reason to go to Mykonos?

Going to Mykonos doesn't offer any particular advantage compared to other islands unless you like to party and spend a lot of money.

IF you start talking about Mykonos, it's probably because you fell for CHAT gpt, which can i remind you is not a human with experience, it simply scoops up slop & serves it up... it never suggests what we vets recommend, doing athens Last ... and it will always recommend places that are most frequently mentioned - which doesn't mean they are the best advisor (i.e. Mykonos). Try to wean yourself off AI zombies, their algorithm is to recommend what is most popular, not what may be best for you.

Thanks Janet and Jo Lui! I am getting the sense that it really is recommended to cover islands first, then mainland. But if I wanted to end in the islands, would it not still work to plan for a buffer night or two in Athens before flying out, in case? I'm also realizing that trying to include time in Paris before heading back is not necessary...it adds cost and I can instead use the few extra days to make the time in Greece more manageable...so I'll arrive and leave from Athens and/or Santorini, depending on how the itinerary ends up looking...but the main flights will likely need to be to and from Athens.

The current focus...as I have been looking more closely at the RS itinerary for mainland, I am struck by how much time is spend driving and in such a condense stretch...probably too intense for me (see below for most recent edition), and a bit ironic as there is advice in the book to avoid "one-night stands" (meaning try to stay in once place more than one night), but there are a few one nighters in there! I think the only way it would work is to either cut out some of the more northern locations (Meteora), or find smaller places to visit between it and Athens - Delphi, Delphi-Meteora, and Meteora - Olympus. Else some of those driving stretches add up to 6 hrs in a day. A bit much. I'd welcome suggestions on little treasures and possibly overnights that could be incorporated along the way (even if not right on the main route)!

I recognize that an alternative would be to just spend more time visiting more islands in a cluster (Cyclades)...but I feel like I want to see both mainland and a sample of islands...

I think the Rick Steve’s recommended itineraries are often too aggressive for the independent traveler. I use them as template that should be revised. I usually spend more days than he recommends. His itineraries are tightly connected to his tours where someone else does the driving and planning.

Since you're flying from Paris, in my opinion the most efficient way to plan your itinerary is to:

1 - Flight from Paris to Santorini. There are one or two flights a day from Paris Orly with Transavia (Air France's subsidiary) or one flight every Saturday from Paris CDG with Air France. Orly Airport is closer to Paris and easier to reach than CDG. It's a 3.5-hour flight, the time difference in Greece is +1 hour. Like many French people, we have sometimes taken a direct flight from France to Santorini, not to stay in Santorini, but just to travel to other islands by ferry without going through Athens.

2 - Take a ferry from Santorini to Naxos (8 ferries per day - crossing time is 1.5 to 2.5 hours depending on the ferry).

3 - Either take a ferry to Athens - Piraeus (8 ferries per day) or a flight to Athens Airport with Aegean or Sky Express (approximately 10 flights per day).

4 - Rent a car and start your trip in the mainland.

5 - End with a 2 or 3 nights stay in Athens before taking your flight back to Paris.

I would add at least one night in Naxos if you want to stay there to explore it. Otherwise, that only gives you two full days for the largest of the Cyclades islands, which certainly can't be visited in less than 4 days.
If you only stay 3 nights in Naxos (or any other island), day 1 will essentially be packing, check-out, transfer to the port, waiting for the ferry, ferry crossing, arrival in Naxos, transfer, check-in, and unpacking.
Once settled in, you'll only get a glimpse of the immediate surroundings.

Day 4 will be a morning spent packing, check-out, transfer to the port or airport, and travel to Athens by ferry or flight.

So, in fact, only days 2 and 3 are full days.

The RS tour seems very fast-paced, and everything is planned for the tour participants without them having to worry about any logistics, driving, or finding their way. It's not only difficult to do the same route on your own, but it's not necessarily worth following the exact same itinerary.

The RS tour is just a selection of "must-sees.". Are you sure these are exactly the places that interest you, and do you want to spend the same amount of time in each? What if you found a more interesting place outside of this itinerary?

In Greece, we no longer focus on "must-sees" as stops for overnight stays (or longer). Keep in mind that most of the time, you'll only spend 2 or 3 hours max at an archaeological site. So it's just as effective to do a little research and stop somewhere other than these overcrowded spots. And honestly, that's where we have the best time.