Anyone know if its possible to use this kind of glaze/ganache to cover the whole cake - ie ice the sides as well as top? If so, is the amount made...

When I'm working with liquid ganache to cover cakes I tend to make twice as much as I need because of two reasons. One: glazing a whole cake often times takes two coats, depending on the texture of the outside of the cake, and, two: I glaze my cakes on a cooling rack set atop a piece of parchment to catch & re-use "drippings." Depending on the height and width of your cake, and how deep/think you want the ganache, and the temperature of the cake and ganache (i.e.- how quickly it will set), the amount you need is really up to you and said cake. Leftover ganache makes the best hot chocolate, so it's never a waste in my book!