So here is what I did
fly from Chicago to Paris. 2 hour layover then fly to Zagreb. Immediately got a rental car and drove to Plitvice lakes national park. It was night so we got dinner and went to bed we had a room ($45 / night ) about 5 miles from the park. Woke up early and headed to the park. Spent the morning there. It is an extremely beautiful park with a dozen or so water falls. Google "plitvice lakes" Then we drove to split and dropped off the car. Had about a one hour wait for a ferry ($12) to Hvar. Got in around 4pm to port. Hvar is a tiny city. Spent three nights there ($60 per night). Rode electric bikes (too hilly for a normal bike), checked out the fort, walked around the city and the coastline. The water was too cold to swim. June, july, August , September sound like the time to go in the water. Went to cafes during the day. Despite being 65 degrees the sun was extremely hot. Then we took a ferry to Dubrovnik ($16). And got in around noon. We arrived st the port and took a cab to our room ($60 per night) which was on the cliff outside old town. Nice view over looking the city. Google "Dubrovnik old town". This is where some of game of thrones is filmed. Get there early (7 am to 9 am ) or late (after 6pm). During there day there are large Tour groups from cruise ships and ferry day trips that make things congested. We walked the walls surrounding the city. Took a kayak around the coves and the closest island. Some people were jumping off the rocks into the water despite it being pretty cold. It was sunny so the beaches had a decent crowd. Had a bunch of good meals and a lot of espresso. Spent two nights there and then flew from Dubrovnik to Zagreb. Then immediately to Paris. Spent two nights in a tiny hotel room there (much more expensive than Croatia). Checked out most of the touristy stuff. Eiffel Tower, arc de triumphe, louvre. Took a river ride. Went to a converted club in a museum from midnight to 6am.
Overall really fun and easy to navigate trip. Everyone spoke English and was helpful. Drank mostly local wines. USD exchange is pretty favorable.