Flying into Split and out of Dubrovnik (or reverse) is most efficient,
Unless you are going to Montenegro, then flying out of Podgorica to Tivat might be more efficient.
Korcula (3 nights)
Another island TBD (3 2 nights)
Dubrovnik (1 night)
Montenegro. (3 5 nights)
Okay, skip Dubrovnik and for the "another Island" maybe you stay 2 nights at a winery on the Pelješac peninsula and explore the peninsula.
Day 1 after Croatia: Then on to Montenegro. You shoudl be able to ge to Hereceg Novi before lunch, do the tour and have lunch. 2 to 3 hour drive depending on where on the peninsula you stay. Then on to Perast for the tour of the islands and then evening. I like Hotel Conte.
Day 2 after Croatia: On to Kotor for the tour and lunch in Kotor then up over the mountains on the P1 road to to see a prosciutto making house. Try some samples then on to the old capital of Cetinje for the tour. End in Budva early evening. Night in Budva inside the walls.
Day 3 after Croatia; In Budva. Relax day mostly or do a boat tour. Night inside the walls.
OPTION 1 Day 4 after Croatia: Go inland to the Ostrog Monastery and lunch at Sokoline Hotel. Then on to the Tara River Canyon and the Tara Motel MB.
OPTION 1 Day 5 after Croatia: Zip line the canyon or raft the canyon or ….. lots of stuff. Night at the Tara Motel MB
OPTION 2 Day 4 after Croatia: go down the coast to Stari Bar ghost town tour and lunch and end in Ulcinj old town. Night in Ulcinj.
OPTION 2 Day 5 after Croatia: Day in Ulcinj maybe tour the lake take a boat trip. Lots to do, need some input on interests. Possibly a trip to a ancient village with a winery in it. Maybe home cooking day ….. Olive Plantation and sampling maybe.
Day 6 after Croatia head to Podgorica for the flight onward.
Dijana is a lot better at this than I am.