Because the home leg is via Istanbul, extend the trip by 2-3 days and see Istanbul!
Cool city.
If flights aren’t booked yet check return leg from HR to Munich or Frankfurt. Lufthansa has good coverage in this area.
Check that the route to Dubrovnik by car can be done entirely in Croatia, or that the rental agency allows entry into Bosnia. When I was there a few years ago the entirely-within-HR route was not available so the only practical way from Split to Dubrovnik was via ferry. We skipped that.