Hi, Gang!
I have to agree with Debraw: a full suit, no matter what the thickness, is appropriate. Although Hawaii does not have all the soft stinging things that much of the rest of the coral reef world has, there are things that can "get" you.
I do not know what your tolerance for cold is, but I use a 3mil Henderson gold for May-Sept in Hawaii waters (water temp = ca. 79-83 deg F) and a 5mil much of the rest of the year (water temp - ca. 72-78 deg F).
Be sure to do the outer wall of Molokini! And have a great time!
Scorpionfish