Power cables 12V, GND, 5V arrangement and thickness
To make cables routing simpler the diameter of 5V cable can be reduced: it has to carry max 10W so AWG20 or AWG22 is enough.
5V cable (after reducing the thickness) can be routed in the space between the main backplane and 1st aluminium bar (the one closest to the back side of the backplane).
If routing is still problematic we can use single-insulated cables for 12V, 5V and GND. The double insulation in the current design requirement did not come from CERN.
Proposed "flattened" cables routing (still requires some solution to hold cables together):