travelling to Greece from SW Turkey

Hi,
I have a work related meeting in Alanya, Turkey, in September.
My partner is thinking of flying out to meet me near the end of my
work week for a holiday.

We would like to make our way west to Greece - eventually going to
Athens from which we would return.

When I look on google, it doesn't appear there are train tracks in
southwest
turkey. Are there (nice = AirCon) coaches, or is it better to rent a
car?

Is there an extensive network of ferries in the Greek Isles? If so,
is there something like a "pass" that would allow us to go where the
wind takes us, so to speak, or is it better to pre-book everything?

Also, does anyone know if mid September counts as high or mid season?

Thanks in Advance!