One of the challenges was simply tweaking the hair material to look accurate while rendering in a reasonable time. I couldn’t use transparency in the hair shader without at least doubling the render time, and that would have helped with smoothing out the transition between the ear hair and the ear skin. As well, transparency helps with making the fur look soft, so getting the parts with shorter hair like around the mouth to look acceptably soft required a lot of messing around with density, length, thickness, and noise values.
As I hinted at earlier, making the hair look good while moving the underlying mesh for parts like the eyebrows was a hard. That is because the hair’s styling might work well for one position, but another might cause things like hairs randomly sticking out. Fixing that just took a lot of experimentation and brushing the hair in many different poses to fix the odd stray hairs.
Hopefully that provides some useful insight.