WOW! Congrats. I am hoping to be able to post that soon too, next summer is our 20th anniversary and we got married on the Big Island. We have actually been back to Hawaii many times but the last time was 2008.
When on the Big Island, you should try hard to make your way to Hapuna Beach. It is an incredible long stretch of sandy shallow beach that is just incredible. Also, once in a lifetime type of journeys are abundant including Volanos National Park, the astronomy tour to the top of Mauna Kea at night, Waipio valley, (driving down the hill to this valley was very very scary and I dont know if I would do it again cause I looked to my right and saw an old car at the bottom. It took me a few seconds to realize that this wasnt a thrill ride but real life and we could easily end up like that-it is crazy. The beach and valley is unreal tho)
Gosh I could go on and on, there is soooo much to see and do on the BI. Also try to make time to snorkel on Oahu at Hanauma Bay and try if you can to get to Kailua Beach, well worth the drive! Have a wonderful time.