and this is the Short (Back) Wall, 1 required. Note that this is pretty minimally framed. The Blocking should be flush with the outside edge of the 2x4 framing, and the CA Corner should be flush with the inside edge of the 2x4 framing. Toe nailing of the blocking is just fine, its providing a nailing surface for your siding to run horizontally. You can stagger then vertically an inch or so, if it makes it easier, you've plenty of width to play with.