My husband and I are planning a trip to Croatia in late Sept. - early Oct. At this point we are thinking of flying into Zagreb (staying a few days), then on to Plitvice Lakes for 2 days, then to Rovinj for 2 days, on to Split for 2-3 days, Hvar for 2 days, Korcula for 2 days, and Dubrovnik for 3 days -- and flying home from there. We know we can travel by ferry once we are in Split. But what is the best way in the earlier part of the trip? We would rather not rent a car -- are buses the best option? In all my reading I am not seeing anything about frequent trains (which we are used to in other parts of Europe). Would love to get advice about this -- thanks in advance. BTW, we are 67 and 70 years old, want to do some light hiking and cycling as well as exploring cities.
Croatia has a good bus network. When I started travelling there it was not that easy to find out timetables, but I would just go to the local bus station and inquire there. Nowadays there is the https://www.buscroatia.com/ website.
It is still not needed to book buses far in advance though.
I would drop Rovinj from your plan. It is a nice historic town, but Croatia is literally filled with nice historic towns. You do not need to visit all of them. Rovinj is out of the way.
Do Zagreb - Plitvice - Split by bus, then continue by ferries to Hvar, Korcula and finally Dubrovnic. Then fly back from there.
For Plitviice: Stay at one of the hotels near entrance 2, so that you can walk to the park, and then use the internal bus to get around. Note that the busses from Zagreb will all probably first stop at entrance 1. You want to stay on till the Plitvice Jezera stop. If in doubt, just ask the driver.
The bus network is extensive in Croatia. Flixbus is the most popular but I also used getbybus.com to see a few more options. Popular routes did sell out so I would just buy your ticket a day or so ahead of time. You can also check out the bus station for routes and times when you arrive in a city.
I wouldn't call Flixbus the most popular bus network in Croatia. That probably would be Autotrans (now owned by Arriva).
But there are others. The way it usually works in Croatia is that for a given route several companies divide up the services, so that you have a more or less consistent service throughout the day. These buses are used by locals as well, with people just getting on at a busstop and paying the driver. No need to book far in advance. I always just go to the main bus station in town and buy tickets there.