No staples?

This would be good to use in crawlspace, over the fiberglass insulation, if rodents are a problem, as it might be less rodent-cozy since it is so dense. But for your overhead attic area, if that is just beneath your roof, you want to make sure you have at least 2" of air-flow between the insulation and the bottom of the roof. Otherwise, your roof will lose "life" faster. Although more costly, what I am using for just beneath the roof in my attic spaces, is 2" insulation foam board. It is costly and takes precision to put it in, but there will be 2" between this and my roof "ceiling" for decent air flow. If your roof joists are 6", then you could put this in (would need to use wire or twine zig-zagged so it would not fall down), and just make sure you leave 2" gap between the insulation and your roof.

yes - as long as its a little wider than the rafters. If there are some areas where the rafters are a little wider, I used "U" shape romex nail to help hold it in.