Hindsight is always 20/20.In hindsight i should have added some additional studs to bring the wall to conformance.
Cement board is not rated for 24" centers as far as I know. As you can see why. The wall must be flat and flat begins with the studs and the stud spacing.
You have no idea how right you are.Lastly i am tiling with 12x24" tiles and believe the choice of tile will add complexity.
The studs need to be 16" on center.