Capn Smollett-
Believe the hardener is sold separately, much like the West Systems products are. You can get the hardener at
here,
here, or
here. Given summer temperatures, you might want to use the slow hardener, to have a bit more working time—it is the first link above.
If you are fairing something that will be underwater, I wouldn't use the microballon filler, since I believe that the microballoon filler can absorb water. I would use the MAS milled fiberglass filler instead. You can find it
here. I think the fiberglass filler is a bit easier to fair than the cab-o-sil filler.

Hope that helps.