It's good you mention zbrush. Because once again for a stl mesh all you need to do is run the triangulate on you maya mesh and now you can import that mesh into zbrush. Then you can either remesh or dyanmesh to make the all tri mesh into all quads. Although the mesh will be super dense. This is not really a major problem to convert into and stl file.

About texturing and smoothing. Although the third model is all quads those odd pointy shaped poly faces ("kites") going into the corners would cause issue if you tried to smooth because you could not add control loops easily. I'll add a screen shot to show what you would need to do and maintain that topo. As well as a way to make an even cleaner topo.

For uv distribution and painting, especially in zbrush, you want to avoid areas with really dense concentrations of verts and then areas with large spaces. As you move from high vert/uv concentration to low you will find that your textures stretch.

Here are some examples of that third cube and how I had to add support edges and maintain the odd shaped poly faces and another version where I made a small change and have a much better square poly layout that is easier to add support loops.

You can see the second and third images both smooth okay but the third has a better topology (it no longer has those diagonal diamond shaped poly faces). You can see it has a more regular topo after smoothing as well.