2) A contractor friend recommended con-fill for fixing spots where the HardieBacker had not snapped cleanly (corners etc.). From the name, I was assuming that it was primarily cementicious. However, having used it now, I see that it is plaster of Paris based, with some cement in it.
This could be a big disaster when I apply thinset over it--it could soften.... Now I'm hoping that the layer of AquaDefence will make this a non-issue when I'm installing the tiles. However, during the taping phase it could still be a problem. We'll see.
So much advice, so much to learn.... Appreciate all the help.