We spent a week in HI last November - flew home Thanksgiving. We stayed at the Hilton Waikoloa Village to burn off a bunch of hotel points. A couple things to note.
EDIT - just noticed you have your accommodations already picked out... Well disregard but I will leave my review of the Hilton here for others.
Hilton Waikoloa - a huge property that is pretty removed from the action. If your goal is to stay on the property this would be a good place. They have a large lagoon complete with turtles for snorkeling and paddle boarding. For folks who don't like the open ocean it's a decent alternative. Prices are extraordinary (high). Lots of food options though most are average quality. Depending on which tower you are placed it can take you 20 minutes to walk from your room to the parking lot. Lots of cool artwork to see - the property seems to cater to Japanese tourists. If your plan is to do lots of outdoor adventures then this resort should be last on your list. We racked up 500 miles that week getting where we wanted to go.
Ocean sports - diving and snorkeling are fantastic. We always hit up Snorkel Bob on the first day for a week long rental of the good gear. Lots of great diving just outside the harbor - something like 40 different spots. Shout out to Jacks Diving Locker - great crew. There is lots of good shoreline snorkling (2 steps is best) but for a good organized boat trip book with Fair Wind on their Hula Kai boat. Great food, drinks, and the boat is new and faster so they take you to some remote spots. The last spot furthest South was amazing - deep caves and cliffs with lots of sea life.
Night Manta Ray Dive - DO IT! My 14 yr daughter and my wife were really concerned about entering the water at night. Both agree it was the highlight of their trip.
Island Explorations - South past Kona are lots of coffee plantations and the scenery changes to exotic - compared to the lava fields. In between the Hilton and the Kona airport off the 19 is a lava field park. Drive down a mile or so and get out to walk. Literally a different planet. Plan a 1 day drive to the other side Hilo. Drive the Old Mamalahoa Hwy - beautiful scenery - similar to road to Hana on Maui. Bring a lunch to the Kolekole Beach Park - weekdays there's nobody there.
Have a great trip!