As we are proceeding with the schematics and the PCB placing, we are realizing that we will need more than a single PCB to make everything fit. We will then design an horizontal PCB, very much like SpiRose, though ours will be rectangular for budgetary reasons and it will only host our voltage regulators. The interface between the horizontal and vertical PCBs will be three big pads: GND, 3.3V and 5V. Hence, no signal integrity concerns (at least not at this interface). I placed our 12 to 5V converter on Xpedition Layout while conforming to the PCB layout guide of the module.
Furthermore, it appears that the PCB size of 190 by 190mm that we initially chose will be problematic for us to solder the LED automatically: the problem being the width of the PCB. I was going through the process of routing the LED drivers so that we could be stacking five of them on each side of the panel (according to our previous PCB layout idea), but that will have to be abandoned in order to make our PCB thinner. We will put 4 driver on each side and 2 above.