Not sure about airfare price from NJ, but I've found airfare to Hawaii generally more expensive than other destinations of similar distance. I'd not be surprised to find them in the $700+ per person range (and I have only done research from the Western part of the US).
I would plan at least a week. There is a lot to do on Oahu besides the resort. You could even split the trip and do part on Oahu and part on another island. If you are traveling with kids, depending on their ages, plan more downtime than touring time. We spent a week at Aulani last year with toddlers and only left the resort for two days - once to the North Shore and once to the Swap Meet (we did leave for dinners frequently though). That was enough for us as the kids needed naps and were happiest playing in the pool or sand vs. touring. If you are alone with your spouse or have older children, then I'm sure you could do more like visit Pearl Harbor, Waikiki, North Shore, hike Diamond Head, etc.
If you are either DVC or can rent points, that is the best value for room prices. If you have kids, the 1-br villa is very nice as it has a kitchen and a washer/dryer.
