Just gutted the old shower, and made a few observations that I wanted to share, and at the same time ask about Kerdi.

The old shower had no leaks at all, and after removing mud pan and lead liner as well as 4" tile on wall, and what looked like 4" square (~1" thick) concrete backer tiles that was set on mesh attached to the studs, there were no indication of any leaks whatsoever behind the walls.

That is good news of course, but these 1" think concrete backer squares were not sealed, some of them had small gaps that were visible after the 4" ceramic tile was removed...

So my question is in regards to installing the new Kerdi on the walls, how high up the walls does this really need to go?

I'm installing the Kerdi over 1/2" hardie board. And the kit i bought came with 33 ft of Kerdi, and it is not enough for all the walls all they way to the ceiling and the floor and curb.