I just wanna do my roof right, half will be cathedral(no attic) – GreenBuildingAdvisor

I’m in the end stages of researching how to do the roof on my double hipped, 60’s, limestone home, with a chimney and a 3.81/12 pitch. Half of the house will be cathedral style as my ceilings are only 7ft 4in. the other half over the bedrooms and bathrooms will remain attic.  

Currently there is an overhanging soffit and a ridge vent, as well as old hard plank boards as the sheathing. Here is my current unfinished plan.

layer 1:    keep the old plank boards as sheathing, replacing what needs                               replaced.

layer 2:   lay down a vapor barrier, wrapping around and under the existing                       over hang 

                          1st problem is here,  I see most people would then bring the                                   vapor barrier down the exterior sheathing about 8″. how                                       would I do something equivalent with a limestone block wall?                             ive seen foundation tape meant for rock but my rock is not flat                             at all.  

layer 3:    2 layers of 1.8 in poly iso board staggered and taped. would also be                      adding 2 layers under the over hanging soffit and sealing gaps with                    foam insulation and tapeing over joints. 

layer 4:     1/2″ plywood sheathing (can I get away with osb? every penny                             matters in my household, hence me doing the labor myself) 

layer 5:      ice and water barrier

layer 6:      high wind rated asphalt shingles as I get pretty high winds here.  

                              maybe my dumbest question, do I nail the shingles only to                                    the layer 4 sheathing, or all the way through to the layer 1                                       sheathing? feels like I could be adding failure points going                                     all the way through.

Im worried about possibly creating an environment for mold in the cathedral part of the house. Now Ive heard of adding a vapor diffusion vent by pulling layers 4 and 5 back about 2-3 inches from the peak and adding a permeable peel and stick layer there to allow for layers 3 and 4 to breath and vent out any possible moisture.

Would this be applicable to my situation? Would I be adding a ridge vent directly over the permeable peel and stick? Would this actually just increase the likelyhood of moisture in layers 3 and 4  through sideways rain and humid days (humidity gets pretty high as I have a creek at the bottom of my drive and am next to dense woods).  

I am open to all suggestions and thoughts on every aspect of this project. Also may be good to note that I am zone 6a but have seen zone 5 winters since moving in. Also while im a ways out from doing this, anyone have suggestions on sealing windows on a limestone home? Im well versed in the methods of a sheathed stick built. 

Also no pressure but my great grandparents who built the home may come to haunt me if I mess this up.