Itinerary Advice

For Crete I would figure out where you want to go before assuming you want a car. We spent 7 nights in Crete before renting a car. We spent four nights in Chania and then took a bus to southwest coast. We then took a ferry and spent one night in Agia Roumeli and two in Sougia. We then took a bus back to Chania where we rented a car. You could spend a lot more time on the southwest coast than we did.

It also would be more efficient to rent a car from airport when you return from Paros and visit the Peloponnese before Athens. It would save you a night near the airport before flying home that you could add to the Peloponnese.

Looks lovely, of course you will need to sort out transport specifics to make sure everything aligns.
Depending on your arrival time in Athens after Paros, you could head off to the Peloponnese immediately, as Nafplio is a short drive. Then you could put all of your Athens time together at the end and not have a separate one-night stay. Not a big deal, but nice if you can avoid it.

Good advice already provided. If you rent a car when you arrive in Crete the chances are the car will sit in a parking lot while you enjoy you stay in whatever city you flew into. Particularly if you fly into Chania. It will take you at least 2 days to discover Chania. Most of the locally owned rent companies will deliver the car to you. We have used Autorentals Crete several times. Its locally owned with great service.

Thank you so much for your thoughts. Now rethinking the car hire in Crete and spending more time in Chania. Very good to hear from experienced travelers.

Just for fun here are some images of Chania.
Chania 2022 https://www.flickr.com/photos/stanbr54/albums/72177720299646015