Does this sound like a more or less workable itinerary?
The first leg I'm considering 1 evening and 3 full days in Maui, staying up north or west. I'll probably drive to the south side from early morning one day and include Pua'a Ka'a State Park for a dip in the pool by the falls, then drive on to Hana for lunch and Red Sand Beach and then get on to Haleakala for the evening. The other 2 days, we can relax and not move about too much (perhaps go to Waihee Ridge Trail and Nakalele Blowhole).
Then I'd move on to Big Island for 3 days. (landing early morning in Hilo and add 2 full days). Lots of things to see so probably 2 days full driving: Waipio Valley Lookout, Mauna Kea Observatory, Akaka Falls, Onomea Scenic Drive, Chain of Craters Rd, Thurston Lava Tube, Kilauea, Black Sand Beach and Green Sand Beach. I'm not sure what is worthwhile on the Kona side? If I find something there, I could consider to hop from there to Kauai instead of flying out of Hilo.
Kauai I want to spend at least 3 full days, if not 4. Bucketlist contains Waimea Canyon, Pu'u Kila Lookout, Kalalau Lookout, Kilauea Lighthouse, Opaekaa Falls, Wailua Falls and Spouting Horn.
The last 3-4 days then we're off to Oahu. I think we'll stay on the north shore so we can more or less pick & chose what to do with a beach nearby. It seems the drive south to Honolulu is about one hour so that's manageable. in the north I'm looking at Waimea Beach, Waimea Falls and Banzai Pipeline. In the south I'd like to see Pearl Harbor, the National Pacific Cemetery, Waikiki Beach, Diamond Head, Hanauma Bay, Makapu'u Point and Nu'uanu Pali Lookout.
Thanks for any input / advice.
How would I best go about regarding car rentals? I've read somewhere that some companies offer multi-island rates, but I can't seem to find anything.