Home interior air/vapor barrier selection – GreenBuildingAdvisor

Hello, new member here, I’ve read a lot of good information off this site.  I’m building a post frame / pole barn style home and am looking for guidance on proper air/vapor barrier selection for the exterior walls.  We actually purchased the home in an uncompleted state (structure is complete and dried in, no interior finishing has been completed).  While there are a few things I would have done differently, overall it is well built.  The home is located in climate zone 5 (West Virginia, right near the tip of the Maryland panhandle).  The home has exterior metal siding and roof (agri panel) and traditional building wrap.  The roof also has styrofoam insulation under the metal, I’m guessing ~1/2″ thick.  I am insulating the exterior walls with 1.5″ thick rockwool boards cut to fit in between the horizontal wood girts and then 5.5″ thick rockwool batts to fill the remainder of the wall cavity.  This should be ~R29 with minimal thermal bridging.  I intend to put an air/vapor barrier over this on the interior side, from pole to pole (~8′ spacing).  I will then install interior horizontal girts and then drywall.  My utilities (electric, etc.) will be ran in the 1.5″ cavity between the back of the drwyall and the air/vapor barrier.  I’m struggling with determining the appropriate barrier here and could use some advice.  I believe since my exterior metal siding is practically impermeable, I should allow for some drying potential inward.  I’m currently leaning towards Certainteed Membrain as I believe it will serve as an air barrier and prevent most vapor diffusion, but still allow inward drying.  It’s also much more affordable and easier to purchase.  I’ve also seen Intello plus and Siga Mijrax, etc. but the differences start to blend together and it gets confusing.  What’s the right option here?

Additionally, I’m not sure what to do on the ceiling.  It is a slightly vaulted scissor truss ceiling, with traditional attic space and soffit/ridge ventilation.  Currently planning to use two layers of R30 rockwool batts, but that may change depending on how difficult install goes.  Either way, it will be a high R value, just might end up being something else like blown cellulose.  We will have tongue and groove pine for all ceiling.  I know air leakage through the T&G will be an issue if not addressed.  Can I use Certainteed Membrain (or one of the other smart air/vapor barrier products) on the ceiling behind the T&G pine to serve as an air barrier?  Or something else?  I don’t want to install a drywall or plywood backer if at all possible as the ceiling is already fairly low and the additional cost/labor.  I don’t think I need to worry about inward drying for the ceiling being a traditionally vented attic, but certainly do need a good air barrier.

Thanks in advance for any guidance.