Here is a short "making of" video I created of how I set up my 2D facial textures ready for animation. I set my textures onto a surface shader instead of a lambert or any other shader as it is one of the render passes I will be using.
There is a total of around 30 facial texture variations for this character which I designed, modelled, textured and rigged.
Textures resolution : 4096 x 4096
I also used this same set up for my main character which contains over 100 facial texture variations.