Hello, I am remodeling my house. I took down all the sheet rock and have bare walls now. The house has the siding then it has rigid foam board (not sure how thick but it looked decent - its blue if that matters) then I have the vapor barrier (I think that's what the plastic is) then its the diagonal wall boards then the 2x4 wall structure. The wall boards are slightly spaced from one another (photo below). Do I need to fill those gaps in some how? Also I want to use Roxul R15 in the walls would that be enough to keep my house warm in Maine? When I was pulling the old insulation out it looked pretty nasty and looked a little compressed and our house was still pretty warm. Also the idea was brought up to extend the exterior 2x4 to 2x6 but if I do that to the entire house it will take away sq footage but it will also allow me to put in Roxul R23. Is there anything else I should do? I dont know much about insulating but I do know I need to get it up before winter hits. Also heard something about interior vapor control? Whats that?