Confused on Insullating Converted Covered Deck – GreenBuildingAdvisor

Hi all. I am hoping for guidance on the best way to insulate a converted covered deck. My understanding is that this deck was built with the intention of it being converted to conditioned living space at a future date. I am now in the process of doing said conversion.

Details of the structure:

A) I am a few miles south of Charlotte, NC in zone 3A.

B) The structure was built on a vented crawl space. I am not sure the technical term, but it is cinderblock on the inside with brick on the outside (no cinderblock is visible outside).

C) There is a vapor barrier on the dirt floor of the crawl space. There is approximately 3ft of height from the dirt floor to the underside of the 2×10 floor joists.

D) The walls of the structure are 2×6, although ~50% of the wall space are windows.

E) The roof is about a 2.5/12 slope “shed style” and unvented, with a metal roof. The rafters are 2×8 and there are 3 approximately 2×6 sky lights.

F) I intend for this area to be heated and cooled by a mini split.

Specific Questions:

1) For the ceiling, because it is a “hot roof” with no vent, I think I need to do everything that I can do to air and vapor from entering this area? Adding a vent would have been ideal, but it is not possible unfortunately. I had considered a closed cell foam, but am now leaning toward rockwool. If I go the rockwool route, would I need a vapor retarder on the room side of the rockwool?

2) For the walls, likewise, I am thinking rockwool would work here. Would I also need a vapor retarder on the room side of the rockwool? The outside of the walls are plywood/osb with a tyvek wrap, with HardiePlank cement siding.

3) For the crawlspace, encapsulating it sounds like it would have been ideal, but given that it will be conditioned with a mini split, this is not a feasible option. It is a small enough space that I am planning to insulate with batts between the 2x10s. From my research, it looks like air sealing the rim joist will be very important, but I am confused on the usage of the rockwool. Because they are 2x10s, there is approximately 9.5″ of space that I can fill. When I called the manufacturer of Rockwool, they said that I could use the rockwool that is made for 2x8s and leave a air gap between the top of the rockwool and the bottom of the subfloor. Meaning, the rockwool would be flush with the bottom edge of the 2×10. Friction fit to temporary hold and then put a layer of foam board over the entire bottom, being sure to tape the seams, to hold it all in and provide a vapor barrier. Does this actually make sense? I am concerned the air gap my allow critters easier nesting space, if any get in some how. Also, does it make sense to have the foam board act as a vapor barrier? They make a rockwool made for 2×10, but of course it is not available. I could try to combine some other smaller sizes, potentially compressing some of the rockwool to fit. Energy wise, this is overkill for my climate area (3a), from an R value perspective, but it is a small enough area that the cost will be marginal.

4) On the inside, the area will likely be used as any conditioned part of the home, most of the time, but given all of the windows, there will be periods of time where all of the windows are left open and the humidity in the area may rise. In a bad case scenario, I could see someone forgetting to shut the window and rain coming in. I am thinking of using purple board on the walls and ceiling, to help mitigate any of this possibly happening. Other than costing a little more, is there any downside to this approach?

I have been driving myself crazy trying to figure this all out. If you could lend any guidance, I would be so very thankful.