Plitvice and Zadar are two of our favorite places. Plitvice might be my favorite place on earth. Just make sure you get tickets online ahead of time. Zadar has the sea organ. Go to YouTube to look it up. Sitting there watching the sunset over the barrier island is amazing. For the islands , I would suggest Hvar, but spending time in Stari Grad instead of Hvar town. I prefer Split to Dubrovnik, but would not spend more than a day or two there. Just so many tour groups going through the palace. We didn't go to Krka National park, but it looks incredible. Also didn't spend time in Korkula, but have heard great things about that while not on the coast, Zagreb is very underrated.
You can fly into Split, Zagreb, or Dubrovnik We took the bus down from Venice, and then also a bus from Zagreb into Krk.
Amy specific places that you are thinking about that I missed? We greatly love Croatia. If it weren't for aging parents, we would have already moved to Zadar or Krk.