October trip to Greece 1st timers

What do you mean by Rick's plan--a tour itinerary? I see a big difference between doing that with a tour versus solo--I'd go much slower without the guide/transport.
Once you decide if you want to include an island or not, it comes together quickly. Hubs and I spent 11 days among Nafplio, Kardamyli, and Zatouna in the Peloponnese by car, capped off with a day in Athens (I will be coming back to Athens again).

Thanks for the response. By Rick's plan, I mean both his organized tour and his book. I have his book (online version). His recommended sites are similar to those in his organized tour. I wanted to know if anything should change based on the weather in early October.
What island do you recommend in October?

I don't recommend any island, unless that is what you want to do. For my first trip, I went with the mainland. My second trip will also be mainland, but I hope to get to some of the islands eventually. I find including them eats too much into my limited vacation time (also usually 11 days). I love Rick's ethos, but I like to choose where I go myself.
Early October should be pretty nice--I'd go at that time of year in a heartbeat.

It all depends on what your interests are. We’ve done the BOG tour, it’s 14 days and pretty fast paced but a good starting point. In my opinion, you really don’t have time to do the mainland and islands, too.

What island do you recommend in October?

Early October is a perfect time
As for the island it's up to you to choose, but you will need a few extra days if you want to go to an island other than Hydra included in the RS tour.

Hydra is an island in the Saronic Gulf which is not representative if you are looking for the typical island with whitewashed houses and blue domes, these are in the Cyclades Islands.

https://www.visitgreece.gr/islands/cyclades/

Thanks for all of the responses. What do you think of this itinerary? I believe it's a little too intense. I'd like to cut something out. Perhaps Meteora and spend an extra night in Monemvasia just to slow things down a little.
Day 1-Land ATH at 3 PM. Take 6 PM flight to Santorini or stay in Athens
Day 2-Santorini
Day 3 Santorini
Day 4 Fly back to ATH and get picked up by private tour by George the Taxi Driver for tour of Peloponnese. Sleep in Nafplio
Day 5 Sleep in Monemvasia
Day 6 Sleep in Olympia
Day 7 Sleep in Delphi
Day 8 Sleep in Meteora
Days 9-11 Athens
Day 12 Fly out of ATH

Our plan is to visit all of the main sites. In the Peloponnese we will have the van transport for just our group.

You are spending just 1 night at several locations which makes it virtually impossible to have any time at each of those locations.

You'll be driving long distances for each location which eliminates times on each stop.

In addition each move involves packing/unpacking at each location, settling in, getting acquainted with where you are, etc.

The minimum time spent should be 2 days at a location.

Since most of your locations are in the Peloponnese I would add extra time to any of those locations and eliminate Delphi & Meteora.

You're not taking into account travel time. So on your one night stays, all you are doing is traveling from one place to another. Looking at a place for 1-2 hours, sleeping at the hotel and leaving the next morning. Not my type of vacation.

I agree with others. You need at least 2 nights in each place and that means you may need to cut out Delphi and Meteora.

If you have 14 days, take the RS Best of Greece tour. You'll miss Santorini and Meteora though.