RJP: you'll find it HOT HOT during that time. Chances are, even a 3mm may have you a little warm, especially if you're used to colder climates.
As for recommended ops: you'll find that Hawaiian Rafting Adventures will deal better with your technical inclinations than Lahaina Divers. The folks at HRA are into rebreathers, doubles, that sort of thing, and will likely be able to accommodate whatever desires you have for mixed gases, etc. I've heard of people having trouble getting anything except AL72's from Lahaina Divers (despite them advertising that they are available for an increased price).
You may also consider diving with B&B (if you talk to them ahead of time, they may be able to arrange for some sort of technical charter that finds you on some sites most tourists don't get to see due to their being in challenging locations or deeper than recreational depths). You will also find Northshore Explorers to be up your alley.
Personally, given your level, I'd avoid the resort operations -- their rates are to make up for the fact that they're adult babysitters... most of the divers they see hardly know how to assemble their gear, let alone use it.