For what it's worth, the template I use for send to device is:
Code:
ebooks/{author_sort:sublist(0,1,&)}/{title} - {authors:sublist(0,1,&)}
Both the author_sort used for the directory name and the authors appended to the file name are shortened to the first name in the list (the sublist bit). The author names are visible to the Kobo GUI.
I ran into the shortened path issue years back with an anthology that listed 42 authors in the authors list. It made for a rather interesting entry in my library.