We just got back from 4 nights at Aulani (first time for us too) and definitely wished we had put at least one night in Waikiki. It was a mild pain to go back and forth and plan around the distance. If Giovanni's is on your list, the Waikiki location (in the food court above the HMart) was the perfect small detour for lunch, and groceries/snacks pickup coming out of the airport rental car, before heading to the resort. Their cut fruit platters were a lot cheaper than ICM, and great to have poolside and at the beach. We also really enjoyed using our waterproof phone holders that we got beforehand from Best Buy, in the lazy river and lagoon. You can log in at 3pm local time (recreation.gov) the day before to get $1 Arizona memorial tickets at Pearl Harbor. They go within minutes, though if you don't catch the first wave, check again when the hold timer runs out for people (15 minutes I think?) as a few more will pop up. Was pretty easy to get next day Diamondhead tickets as well. Hope you guys have a great time!