Re: Tiling a backsplash
Get some unmodified thinset, the kind for setting stone, add masonry sand until it's a stiff mortar, and float the wall with that. Thinset is very portland-rich and can take extra sand. Use bonding agent on the wallboard.
You could as well use Structolite basecoat plaster for floating. A 3' or 4' Darby float is probably all you would need tool wise. It's a magnesium straightedge for rodding browncoat plasterwork.
Remove not the ancient landmark, which your fathers have set.