And you are right - Sierra, drysuit, doubles.
I'm assuming you are bringing the Sierra, are you renting the doubles?
I can't tell you how done I am mentally dealing with doubles and a stage in locations where if you want anything other than a single AL80 with their banked gas, they look at you like you are from Mars!
There are very few dive shops here that get more than a handful of calls per year regarding doubles, but there are a few that can help you out if they feel like it. For 99.9% of the diving done in Hawaii there is little need for more than the 100 cft's with air, 32% or 36% that you can get on any island with proper prior planning.
Divers in that other 0.1% should expect being looked at like they are from Mars; isn't that one of the reasons for being a 0.1%er?