I have a character and would like to add Sunglasses to it. Would it be best to track the sunglasses after with tracking markers or can you add them to the character elements in your psd file
There are two ways. First, edit the original artwork following the guide lines for layer naming or second, track the head movement of your rendered character and add sunglasses as another layer in AE. The first option is easiest.
You should just be able to add a new layer in your Photoshop or Illustrator document that is within the Head group. It should automatically transform the glasses as you interact with the face tracker. This same method could be applied to add scars, face tattoos, pimples, freckles, etc. Good luck!