Nice video, I only have 2 issues with it:
1) It doesn't really matter what grid size you use to build geometry; the imortant thing is to make sure it fits nicely within the largest grid size possible for that piece of geometry. If you use tiny cubes to fill up a cube of a larger grid, remipping will fix this for you (yes I just made this video for you guys):
Of course it is easier to fit geometry inside a larger grid if you simply use that larger grid to build it in the first place, so what you say holds true in the end.
Keeping things aligned with as many grid sizes as possible is desirable for the reason of easier copy-and-paste as well (as many as possible = from the smallest to as big as possible).
2) "wtr" is the number of triangles that have to be rendered, not the amount of cubes in the map. With the outline view turned on you can see those triangles layed over a cube's surfaces.