IMO, yes. Parking will be free assuming you're using your DVC points.
We also honeymooned in Hawaii. We spent 6 nights at Aulani, 3 nights on Maui, and also spent time in Waikiki and Kauai. We had a car during our Aulani portion and during our Kauai portion, and both came in handy. We opted not to have a car in Maui due to the plans we had there (we were able to utilize the hotel shuttle), but I would get a car next time if we visited Maui again.
At Aulani, keep in mind that there's very few things in walking distance and everything outside of Ko Olina is only accessible via highway. Uber is not always reliable in that area either. If you want to experience Oahu, you'll want the flexibility to actually see the island and get out of the curated tourist community of Ko Olina.
I would start planning now and get a sense of what you want to do, and book as early as possible. We started planning in November for the following September, and booked as early as we could. Certain things have logistics to consider - i.e. Diamond Head is best done early, Pearl Harbor needs a full day if you're not able to secure an advanced tour time (a full day because you won't know your tour time until day of, not because it takes a full day to tour it), Kualoa Ranch tours have limited capacity and sometimes are only offered once per day or a few times a week, etc.
For the luau, I would suggest looking at the ones on Maui, depending on where you're staying there. The two in Lahaina (Old Lahaina Luau and Feast at Lele) are two of the highest rated luaus in Hawaii. We did the Feast at Lele and loved it. I think we booked that about 6 months in advance, and they assigned tables based on the order you book in. Because we were one of the first to book, our table was front and center.
