No Humpback whales in Hawaii in August, sorry. This year the first one was spotted towards the end of September. One week on Oahu is a long time. Depending on arrival time, I would spend three or four nights on Oahu and the remainder of my trip on Maui. But if your staying on Oahu for free, well, free is for me!
As for Haleakala, sunrise is nice. That said, it is nice no matter when you go up. Everytime we are on Maui, we head up.