Congrats on planning your Hawaiian wedding! Such a beautiful location. If you're not familiar with the islands, finding a WC from Hawaii to help with the plans is probably a good idea. There are a lot of great places that will do both your ceremony and reception. If you're hoping for Luau there are a bunch that will hold your ceremony earlier in the day and then offer the luau for the reception. I'm not sure which ones are completely private luau's or not, but with 50 guests you'll take up a good amount of space.
We're heading there again in just a few weeks and we can hardly wait for a few days of R&R while we're there. Best of luck with the plans!