How far in advance is required to charter the dive boat? What documents are need to obtain scuba gear?

The only dive boats on Molokai are operated by Molokai Fish and Dive. Usually a couple days notice will be sufficient lead time for SCUBA charters. Scuba gear is furnished for all of their dives and you will need to present a PADI (or similar) Diver’s certification card. You can find more details here – http://scubadivemolokai.com