I admit I've already drawn many 3D on Sketchup, but I really didn't know how to do this one... After some research, I went on a tube shape in which I drew circles. By deforming these circles I was able to arrive on the shape I was looking for. To adjust a dimension based on the center of the shape, simply hold down the ctrl key.

For the front, I just placed a flat face using the "Intersect Faces" option. Here is the result :

And here is the rendering on Sketchup with a little color and a lot more spines :

And ready to print with CURA (some spines are missing...)

The tricky part here is tilting the HEADER 11 Pin by 15° so that the top PCB follows the slope of the hedgehog. I will try to design a small tool to facilitate this step.

As this is a prototype, there is a lot more connection here than there should be. I did a lot of tests... 

All that remains is to make a small interconnection PCB. The prototype works well but lacks a bit of aesthetics with all its cables. 

Here is an idea of the minimum and maximum manufacturing cost of the project (for one unit)