Booking paid activities/excursions at Aulani

[cruisehopeful]

We're looking at visiting Aulani (DVC rooms) and I noticed there are a lot of activities available. Since we've been to the island several times, letting someone else drive and arrange everything sounds very nice. Do you book everything before your stay and how far in advance? Do they have a concierge desk where we can book stuff after we arrive? We're probably going to do the Spa, the Luau and a couple day trips that visit the other side of the island. We might possibly rent a car for a day to be able to take our time on the North Shore, but other than that, being in a tour group sounds appealing.