Hey @Bickity
we also have an application that creates folders in the user profile at start-up and then fills them from the network drive if it does not already exist.
We have helped ourselves by having already created the pre-filled folder in the default user profile in the Master VM. This takes longer to logon to Windows because the User Profile Service always copies the directories over. But this is faster than fetching them from the network when starting the application.
There is no minimum or maximum of folders that must exists. Try to create predefined settings as comfortable as much for the users and don't forget the logon time when doing this. DEM ist perfect for this task.