Starting to plan a honeymoon to Hawaii in 2020. Originally had planned on only going to Oahu as I am a big Lost fan and it seemed the easiest to plan. However, after doing some research I want to add Kauai to the trip. I am flying from Boston and plan on being in Hawaii for 8-10 days. I have Hyatt points and 2 free night certificates and a non-flight budget of $3000.
3-5 Nights in OAHU staying in Waikiki beach area without a rental car.
3-5 Nights in Kauai staying at the Grand Hyatt with a rental car.
My questions are is my rental car plan the right one (Oahu without and Kauai with one)? Is 8 days enough time for two islands or is 10 necessary? Any help would be greatly appreciated!