Are you creating simple cuboids (with 6 sides) that you want to texture or 3d objects comprise of multiple cuboids that you will (I suppose) move apart?
On your last example pic (with the interesting green guy). I can see that you have 9 faces per side of the cube (or perhaps 24 cuboids altogether)?. As I can see the seams between the faces, I am guessing this object is still actually many separate objects or faces?
You can combine it into a single one with Probuilder and there will be no seams.
If you don't need each cuboid to be many separate cuboids you could either delete all the inside faces or I can (try) and show you how to build a single object in Probuilder with only 9 faces per side and to whatever proportions you want. i.e. one that looks exactly like your picture but one PB object but no seams and pretty cheap as an object and very quick and easy to repeat in different dimensions.
You would still be able to texture each individual face (or group several faces for one texture) etc
You can do it without subdividing (or any seams) with a cube and shift click extruding into a cube that is 3 faces x 3 faces for each side. You can either extrude them to the correct proportions as you go or push and pull afterwards.
This is much easier with ProGrids too - it makes it easy to push and pull to exact proportions will maintaining the overall size of the cuboid.
Not going to get a chance today, but I could post an example tomorrow if its of any use?