That's plenty. As I recall, I repaired one in the wheelwell and don't think they were even that. You'd rip it out of the surrounding sheet metal before you would damage that. As for the bolt, I'm not sure of the thread size, but they look bigger cause they are shoulder bolts and have an oversized hex head. There are different lengths for different positions. I think the ones in the center hump were longest cause they sit down in.
