The screws you have that are stripped, take a cutting disc on a grinder, cut a + into the head, then hit it with a hammer and a cold chisel, as for the insulation, there will be the same fiberglass throughout the roof. The top insulation is where I found my mold, so I'd recommend a respirator even if it is a large particulate one from a hardware store and safety glasses. Keep the kids away until it is out and you have cleaned it good!
When you cut the remaining ribs for your roof raise, get a 7" cut off wheel for your circular saw, that way it is a straight and smooth cut.
Great job so far!