Hi there, I am converting a barn into a guest house and wanted to get some input on whether or not my proposed wall layers will work (I.e., will I be creating a moisture issue, etc.). Layers:

1. Shingles 
2. House Wrap
3. Plywood Sheathing 
^(note I will be replacing the existing wrap and sheathing eventually with zip system)
4. 2×6 Mineral Wool Batts 
^(note, 2×4 Wall furred out with 1” rigid foam and 1” wood strips)
5. Drywall & latex paint

Key questions I have: 

-Do I need a vapor barrier between 4 & 5? If so what kind and thickness? I’m in Maine if climate matters. 

-Will the eventual zip system install (replacing 2 &3) create any issues? 

On a side note I also have a lot of 2” thick rigid foam insulation that I got for free – could that be useful here? It was cut to fit stud bays by person I got it from, but I’m unsure how to use it effectively. 

thanks!