Flying to Hawaii generally takes a long time. We are Minnesotans - it took us about 8 hours one-way. We found after a couple of trips that leaving EXTREMELY early in the morning is the best to get there. Hawaii has sunset much earlier than we would expect - therefore, if you leave early, you have decent chance of getting to your hotel in the daylight and in time to see your first sunset - a thing to remember.
Our first trip got us there after dark (9 pm local time). This was about 2 in the morning Minnesota time - this left us pretty crabby and not in a mood at all for getting a car and trying to find where we were going. In fact, both of us kept waking up in the middle of the night feeling like we were still moving on the aircraft.
We also found returning with a flight that left at late evening was very good - you basically slept the way back and it gave you an extra day on the island.
I do a fair amount of travel for business and have rented plenty of cars - but renting them in Hawaii is a WHOLE DIFFERENT EXPERIENCE. You'll have to take a bus from the airport to the car rental (you and 250 other people that were on you're aircraft). Then you'll get to stand in a line with those 250 people waiting to rent a car from 1 of the 6 registers staffed with a local with an island work attitude. Expect from the time you get your luggage to the time you are in the car to be well over an hour and likely two. Expect this will drive your bride crazy - she's in Hawaii and waiting with a stack of luggage for you to get a car out of the cattle car line.
Once you get the car - driving in Hawaii is generally pretty easy. Most people are respectful and drive at reasonable speeds. There are very few roads, so getting lost is generally difficult, however, in Honolulu it can be easy to confuse the roads with the Hawaiian names (was that Mililani or Manono street).
Basically the airport and every street corner has a stand full of brochures and coupons for reduced price activities. These are worth getting, reviewing, and saving some dough. Virtually every hotel also has a free morning breakfast with a activities group or person who reviews their recommended activities and company to use. These are worth the 1/2 hour and generally have some pretty good free food.