I've installed foam board along the exterior walls of our basement where I'm building a guest room. I've framed the 2x4 walls along the foam board. Soon I need to insulate those walls. I bought insulation already but it has a backing. Now I'm thinking I should have got non-backed so I don't create a "vapor trap" between the foam board and sheetrock. Should I use what I have?

My parents just bought a house. My dad, a disabled vet spends most of his time in his workshop. His new workshop is a 700 sq ft steel outbuilding that has no insulation. I have a local AC company installing a 24k BTU ductless A/C to replace the pitiful window unit hes trying to cool it off with now, and i have 30 r30 bats of fiberglass insulation on order from Lowes for the roof, and i am going to be painting the roof with Elastomeric paint but i need some advice. i have been doing research on radiant barrier insulation, that its best used in between the framing and the steel paneling to prevent the transfer of heat. Obviously its too late for that since its fully built and im doing all this work myself and theres no way i would be able to deconstruct the building. My question: Im getting the radiant barrier insulation for the 2 roll top doors, 1)would it still be effective inbetween the rafters before i put the fiberglass bats in 2)if it is, should there be an air gap (some of my research says there needs to be an airgap, some says right on the bare metal) 3)since im doing this myself, what would be the easiest, most cost effective way of attaching it since the studs are metal Also, installing the fiberglass bats, my plan was to predrill holes in the rafters and put screws thru the plastic holding the insulation in. 1)which would be better, plastic sheeting or housewrap so it can breath? (i live in florida so humidity is a concern) 2)is there a better way to do it Im on a tight budget so hiring outside help is out of the equation, I work maintenance at a hotel so i have some technical skills, but i have never dealt with a project of this magnitude and any help would be appreciated.