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: