If you're going to be on Maui for a bit (or you're the active/hiking type), I strongly recommend staying two nights in Hana. You'll feel like you have SO MUCH time to do everything you want in and around Hana plus it's just such a change of pace (there's nothing like it in Hawaii).
I would book 1st time slot reservations for Waianapanapa State Park on both mornings so you have options (bad weather, etc.).
You could either do this itinerary the way I have it laid out, or do the Pipiwai Trail/Oheo Gulch on the middle day if you don't care as much about beach/resort time.
And then the third day, you could leave Hana earlier and spend more of the day in Ulupalakua and Upcountry Maui enroute to wherever you're staying next.
