Day 1: Arrive in Makassar
Day 2: Day in Makassar, then night bus to Toraja
Day 3: attend Tana Toraja funeral traditions (MUST do)
Day 4: Batutumonga walk
Day 5: Travel day to Tentena by bus (or by private driver)
Day 6: explore Tentena and Lake Poso
Day 7: Morning private driver to Ampana and at 1pm speedboat to Wakai (Togian Islands)
Day 8: Togian Islands
Day 9: Togian Islands
Day 10: Togian Islands
Day 11: get overnight ferry to Gorontalo
Day 12: Private driver/shared taxi to Manado, then boat to Bunaken
Day 13: Bunaken
Day 14: Bunaken
Day 15: Bunaken
Day 16: Boat to Manado, and taxi to Tangkoko National Park
Day 17: Tangkoko National Park
Day 18: Leave from Manado

Yes, this is a very intense itinerary, but it’s the only way to see everything in just 18 days. If you can, I would personally recommend you to visit Sulawesi for at least 3 weeks. Or if you just have 2 weeks, I would probably advise to skip the Togian Islands, because that is the most remote part of this itinerary, and the most hard to get to (even though one of the most beautiful).