Migrating files structure to the cloud, should all files be copied?

We are in the process of moving all our files (sitting on windows file servers) to Google Drive. I anticipate that the users will be using more of the search capabilities of Google Drive than navigating the path like they are doing right now in the windows file server. Since the file structure has been here for a long time (there are many many files, with same name, with same info, etc..), I don't want users to have difficulties finding the files they want to work on but at the same time have all the files they need.

What are the best practices regarding a file structure migration? Should we copy everything to the cloud? Or should we take this opportunity to clean up and ask a department "leader" to move the files he feels are necessary? Or should we copy only files that have been accessed since X years? What are the options and recommendations?