Some parts of a shelving system I want to model (Balton B III for those who like chrome and steel

are from sheet metal with perforated areas, like
this shelf, for instance.
My challenge is to get the hexagonal perforation pattern into SH3D.
First, I made a texture with two quarter holes (see
1st image, yellow rectangle), repeatedly mirrored along u and v in blender. However, I could not persuade SH3D of the mirroring.
Then I made a non mirroring texture (green rectangle), and had it repeated in SH3D. See the rendered
lower picture.
But:
- Whichever image size I enter in the Texture Import Wizard - it would not let me tweak the aspect ratio, only the absolute size. The wizard enforces a numeric ratio equal to that of the source image, which cannot be square.
- However, when applying the texture the tiles turn out square - no matter what numbers I have entered.
Question 1: how can I make the texture keep its proportions? - I just can't go with square tiles as my pattern demands a certain tile aspect, otherwise the pattern axes are at weird angles.
Making a pre-baked texture for the whole area is not an option, because I have to "perforate" many differently sized areas on a variety of parts with the same pattern, plus the final pattern will be 9 times as fine - requiring several hundred tiles.
Question 2 (maybe another thread?): The upper and lower image use the same texture. When I change the base material's colour, in blender the entire part changes. How can I in SH3D as well keep the base colour of the material in the perforated part, i.e. ignore, or at least transform the texture's RGB values?
Originally, the texture is an SVG. I can easily derive any useful kind of pixel image.
If a potential helper wants to see the .sh3d .obj, .mtl, .png, .svg or anything else - which upload service would you recommend? - Anyway, I'd be grateful for any thought, cause I just
want to do my home in
SH3D for its excellent fitness for the purpose and ease of use.
Forgive me if I was just too blind to see the obvious. (Newbie)