It took about 1/3 of a standard package. I waited two days to make sure it was completely dry and then did some sanding. I followed JiaJem's tutorial on armor to a tee. Two lessons: never sand indoors, and usa an electric sander, if possible. You wouldn't think that sanding something that small would be so difficult, but it really is. So my next cosplay investment will indeed be a mouse sander, preferably something in the $25-30 range.
I filled in the cracks and craters with more Paperclay, let the gun dry, and sanded again. Alas, Christmas Break ended, and I didn't want to deal with trying to sand at my apartment at school. Elena is thus going on hold until Spring Break, when I hope to finish this thing.