Help with itinerary in Greece (Travelling without a car)

In Greece you can take buses into the Peloponnesean Peninsula and fly and take ferries to and from the islands. I found Rick’s Greece Itinerary online. I would delete Hydra, Momenvasia,Kardamyli. He recommends visiting Mykonos and Santorini, the two most visited islands thus crowded and not giving you an authentic feel. Go to Santorini for two nights maximum to see the caldera view and then take a ferry to Paros or Naxos for a much more authentic and real Greek experience. You can return to Athens by ferry or fly.
I have traveled all over Greece several times. I have also traveled in Germany and would definitely choose Greece if you have not been there. I rented a car in Crete and for the Peloponnesean Peninsula as I always rent cars but many travelers do not. You can do this trip without a car!
You mention going from one city to another. Athens is the largest city. Napflion is a much smaller city with
good bus service from Athens. There were tours available from Napflion to the surrounding antiquities, Mycenae, Epidavros. etc. There are other day tours from Athens to Delphi. You can do it without a car by adding small day tours here and there. Same for Crete.
For your itinerary where do you want to go? Athens, Napflion, which islands? First time visitors want to see Santorini and two nights there is enough. It is the most touristy and crowded. Then look at the islands of Paros and Naxos. They are much more authentically Greek.
Greek Orthodox Easter will find Greeks traveling to the islands where they have family. It is a very large and important holiday so arrange your dates very carefully.
There are well respected travel agencies in Athens who would be very, very helpful. Look at Fantasy Travel and Dolphin Hellas Travel to plan your trip, booking you on buses, ferries, flights. Contact them with your questions and they will remove all the stress you may be feeling. Greece is more difficult but is worth so much more! I do not normally use travel agencies but I do in Greece. Coordinating ferry schedules is not as easy as you might think. Stay in small Greek owned hotels too. Some of our best travel memories are from those family owned hotels.

Sorry if I wasn't clear....what I meant by RS recommended itinerary, I was talking about what he recommends in his book. Not a tour.

I'll be in April, so I'll be wanting to go to Greece more for the sightseeing over relaxing on some beach since the weather might be iffy

Rick Steves itinerary Recommendation

I found it online and have rewritten my reply!! Reread my comments above! Our trips have been been heavily influenced and planned by friends who live in Greece and the travel agencies mentioned too.
It is worth the extra steps. You can’t plan a trip to Greece like one to Germany, Italy, or France. Greece is so unique and the extra work is worth it!

While I like to look at Rick's itineraries for inspiration for places to visit I find in practice they are way too jam packed and require too fast of a pace for my liking.

You can absolutely do Greece without a car, I did it first time this past summer. With 2 weeks a combination of a couple of islands and a couple of cities on the mainland would provide a good introduction to Greece at a reasonable pace. I went for 15 days and did Santorini, Naxos, Athens, Meteora, and Delphi. All without a car.

The only thing I'm not sure of is you are going a little earlier in the year. My understanding is things don't really pick up until Easter. Of course if you pick a more popular island like Santorini that probably won't make much of a difference. I'm sure some of our resident Greece experts could shed more light on that.