For stay, I would say it depends on your preference, budget and how many people are in your group. But in most cases hostels are pretty good to stay. And I am not sure about places to skip but definitely try to stay the in plitvice, dubrovnik, and split. They are pretty amazing places. And if you get enough people to join and budget permits, do try to hire a car for road trip between split and dubrovnik (we did from dubrovnik to zagreb and it was definitely one of the best road trips I have had till date with most beautiful views).
Hey Mayank, no people in group as mentioned it is a solo trip. Yes Hostels are the best option and for car hire I think it will be something more spontaneous when I reach there. Also isnt Dubrovnik to Zagreb is very long drive .. haha I am glad you enjoyed it !