Croatia- stuck on trying to figure it out!

With 8 days, you won't have enough time to see more than Split (and nearby), Dubrovnik, and Mostar - so I would just leave it there and not add any more locations. You can easily travel between them by bus. If you want to include the islands, you can use Split as your jumping point. Trogir by Split is very much worth seeing (that could take half to one day). So give yourself 3 full days in Split, at least 2 days in Mostar, and 2 days in Dubrovnik - leaving about 1 day (give or take, could be shorter) for traveling in between. Altogether, that's 8 days.

thank you. We will have a car by the way.

If you have not been to Plitvice Lakes, I really think you should consider that. We went to Croatia, and it was the best day of the trip, if you enjoy walking in the outdoors. Not strenuous, either. Just amazing colors and sights.

I will tell what we did and how long it took, and you can make your decisions from there. Day 1: We took a train from Sarajevo to Mostar, Train left Sarajevo at 7:00am, arrived in Mostar around 9:45am. We dropped our luggage off at the station and explored Mostar till 12:00pm. At 12:30pm we took a bus from Mostar to Dubrovnik and arrived in our hotel in the area of Babin Kuk around 4pm. We spent the rest of the day relaxing around Babin kuk. Day 2: We explored old town Dubrovnik. Day 3: We picked up our rental car at Hertz east of old town around 9am, drove to Split along the beautiful coast line on D8 instead of A1 and arrived around 3pm. We stopped at a small village called Igrane for an hour lunch. After we arrived in Split, we spent the rest of the day within the walls and explored Split and went to Jadrolinija ticket office by the port and got ourselves a schedule. Day 4: I woke up at 7am and went down to the ticket office and bought ourselves a pair of tickets from Jadrolinija for the speed boat leaving at 11:00am, they only sell same day tickets and it was during high season in August so I had to wake up early to buy tickets. At 11:00am we took the speed boat to Hvar and arrived at the town of Hvar at 12:00pm. We spent 3.5 hours in Hvar then took a bus to Stari Grad and spent 1.5 hour at Stari Grad before we hop on a 2 hour ferry back to Split at 5:30pm. We spent the rest of the night exploring the west side of Split that we didn't get to the day before. Day 5: We Left Split at 9am, drove to Plitvice Nation Park and arrived at 11:00am, spent 5 hours there, left around 4pm, arrived at Zagreb and returned our car at 6pm. If we can do all that in 5 days, you can easily cut out Plitvice and add islands around Hvar and Korcula in 8 days.

Consider Split, Mostar and/or one of the islands (Hvar or Korcula depending on transportation connections.) If time, add Zadar.

I have no doubt that Plitvice is amazing but you need to make a call - north or south (including Mostar). It's really not worth trying to do Plitvice and Dubrovnik in one short trip; having a car won't shave off enough time. And for whatever reason, most folks think Dubrovnik is super interesting while there's not much in Split (not true, Split is totally worth visiting and so is Trogir next door). I would suggest reading a book first and trying to figure out what you're really interested in or look under Things to Do for each city on Trip Advisor to get ideas. I was really interested in seeing some of Bosnia (Sarajevo and Mostar), some islands (Brac and Korcula), and the coastline so I limited myself to just Split and south (all the way to Montanegro) - I had 12 days and it was still quite busy.