As far as I can tell, triangles belong to groups and each group can have it's own material. This means that you need to have multiple groups if you want multiple materials, but you can use multiple groups that have the same material.

My gues on referencecount is about on in how many faces an vertex is used.
I second that. I don't see why you would have a refcount field inside a vertex struct for any other reaseon.

It seems like a very vague part of the fileformat. I think your best shot is to just expiriment and try to make it work. You can always solidify the source if someone eventually comes up with some answers.