Hello – we are in the process of building plans for a new house in New York. I have read quite a bit about wall assembly and trying to optimize dollar cost for best insulation for exterior walls.  I saw Jake Burton recommendation and Micheal Chandler sill / wall assembly. 
We are thinking intello wrap, cdx, 2×6 wall with thermal fiber, 1/2″ sheet rock.
Question for the experts.
1. I considered zip-R vs cdx ply and the cost adder is significant. $100 for zip-R vs 25$ for CDX. Is it cost effective to go to 2×8 and use closed cell foam insulation + thermal fiber to get better air sealing?
2. Would the above assembly require an interior vapor barrier?
3. For the exterior of the house, we are thinking of using Hardie backer? Does the wall assembly need any kind of rain screen or can the Hardie go on top of intello?

Thank you very much.