My husband and I are doing the contracting to build our house in central Oklahoma. We're in Zone 3. Our plan right now is to have 2x6 wood framing with open cell insulation and an unvented attic. I've tried to do a lot of research, but I still feel lost, and I'm still a bit worried about moisture issues. I know to make sure our a/c isn't over-sized, and we'll probably get an ERV. What I'm still clueless on is vapor barriers, best sheathing, dew point in walls, insulating the slab and if there's something major that I'm missing.

So far, we've got the slab in and our lumber package is arriving tomorrow. So, first, what kind of sheathing should I order?

Thanks so much for any input!

ETA:
We are still open to what insulation we need to use. We've gotten $9,000 bids for 3.5 inches of open cell foam in the walls, and 5.5 inches in the ceiling. Even when I asked for more foam, every installer I talked to insisted that any more would be overkill. And I talked to 6 or 8 installers! I'm trying hard to read some of the great advice that's been posted here. Should I put some foam board on the outside of the framing? Would I want a house wrap over that? If I do foam board on the outside, how does that affect how the windows attach to the house? Should I just use normal OSB sheathing? If I do foam board on the outside, and I DON'T use open cell foam, what should I use in the walls? Would you still do a flash and fill with 1" of CC and cellulose? If so, which cellulose? And finally, if I don't do open cell in the attic, what should I use?

Framing is starting in a few hours, thanks so much for any help!