After having taken a few days of rest, I started UV- Unwrapping the wooden ‘Cubes’.
This was a lot more difficult than I anticipated, mainly due to the different scales of the wooden planks!
I ended up with this:

I’ll put the rest of the pieces on a separate Map.
It’s not a perfect Unwrap, but I think that I can work with this.
This is what I did (after several failing attempts):
I put all linked duplicates in a different Collection (how I love Collections!).
Then I put seams on each of the unique wood pieces.
So, all of the wood pieces had seams.
Then, in Object mode, I made everything a single user and applied the scale.
Selecting all the wooden pieces which had seams, I went into Edit Mode (another great feature of 2.80!) and Unwrapped them.
Averaged Island Scale and Packed the Islands.
Slightly adjusted the Margin and made a New Image of 8192 by 8192, with the Generated Type set to Grid.
In the Shader Editor, made a New Material with the newly created Image plugged into the Principled Shader (Selected the Principled Shader and pressed CTRL T, thanks to the ‘Node Wrangler Addon!).
Again, in 2.79, this would have been a lot more work!
Unfortunately, I can’t re-establish the Links now, due to the Scaling, but the alternative would be to either modell a lot more planks, or to put a Lattice on almost every plank and use the Lattices to give the planks their fitting shape…