It is difficult to recommend a specific routing without knowing one's travel style. I plan in one direction to not lose one day just getting between two destinations.
In Split , look for apartments actually IN the walls (these were built for soldiers as the walls were built) not just other buildings inside the walls.
I have been told by relatives that parking in Split is awful but I have never rented a car myself in Croatia. Others with more familiarity could give you better information.
Enjoy the planning and the trip, Croatia has many wonderful places to visit and the people are friendly, easy going and interesting. .