You can just paint the Voxels if you want Symbols on the Tools. 
And the Tools do have to be compatible with the World Rendering System, since all of them can be placed in World.
As for a sense of Scale, each Voxel would be roughly 3x3x3 cm³ in size.
Modeling the Tools would be either some other GUI or something involving using Clay to Model it. Unsure how that is gonna be done, but you get some sort of Editor for sure.