DD and my first trip to Hawaii was in 2017. DH had been there before. We flew into Oahu, spent a few nights at Aulani and then flew to Maui and spent a few nights there. Booking the trip as single leg flights was not any more expensive than booking round trip flights.
We dubbed Aulani as "Disney Hawaii" and Maui as "real Hawaii". Don't get me wrong-- Disney Hawaii was wonderful. In fact, so wonderful that we only spent one day away from Aulani -went to Dole Plantation (waste of time), North Shore (shortly), and PCC (cheesy but we loved it)- and then we cancelled all plans to leave the resort the rest of the time because we loved Aulani and just wanted to stay at the resort. Even the lagoon at Aulani is man made (as are the other lagoons on that part of the island). In Maui our resort was on a real beach and we also did the Road to Hana and saw absolutely gorgeous natural parts of Hawaii. You might want to re-think being too overwhelmed to try more than one Island. I was overwhelmed at first too, but I just figured out a hotel on Maui- figured out flights- and then we went to Maui with no specific plans at all. It worked out great. I'm very glad that on my first trip to Hawaii I actually saw some "real Hawaii", as opposed to just the disneyfied version. I'm also extremely glad we spent time at Aulani and I can't imagine ever going to Oahu without staying there at least part of the time.
Also be aware that if you stay somewhere else and just go visit Aulani, you will not be allowed to meet the characters (outside of a booked character meal). You have to have a resort wristband to get in line to see the characters. We saw people get turned away and one time saw some unhappy kids because the family had come over from a different resort and tried to see the characters.