Agreed with gnoop - I despise the 2.5D canvas... Its pretty rare I need to use Zbrush for tiling textures these days, but when I do, its a combination of array meshes and offsetting (under deformation menu). If you work with the Zbrush 2x2 plane, you can place subtools on one edge, then offset them by 200 on whatever axis…
if you use default z brush plane primitive and your target texture is 1x2 you can use 2 and -2 in Array for x axis (using append new button) and 2 and -4 for y axis. Also duplicate the original plane before this overlay scale up. You would be able to use it as a crop factor after you "grab" it , and then texture > crop and…