2D/3D worflow with Blender

I had to combine 2D design and 3D  for a easier animation process...

Here is my workflow:

Final result :

 2 combined passes (2D/3D). I used "dilate/erode" node for keeping freestyle lines the right width when over the 2d textured plane.

2Dpass :  basic setup but with "All Z" checked to avoid Zdepth conflict in compositing.

3Dpass with freestyle setup

 3D viewport: Textured planes are in specific layer checked for 2D pass. 3D body is on another layer cheked for 3D pass.

Shader for the planes:

Shader for the 3d body: