Booking Car Ferries / Island Hopping Tickets

My husband and I are visiting Croatia in June this year. We are flying into Dubrovnik and heading north to Istria. We planned on island hoping at various points on our way north. For the most part, we will need a car ferry. Do you recommend making reservations ahead of time? If so, how far in advance? How busy is the ferry system in June usually? I know it’s not “high” season yet in Europe, so my thinking is that things won’t be as busy. I can make reservations ahead of time; however, last-minute ticketing would also be good in case we’re having such an enjoyable time that we don’t want to leave the area. I would appreciate any information you could give me. Thank you so much. Looking forward to our visit.