Generally speaking, the organization of offline report storage on your file share is independent of how the content is organized within Tableau Server and therefore it doesn't need to be centralized in any one location, but it should be organized so that you can find what needs to be reviewed and then published. I suggest that the content could be organized by any number of dimensions and I don't know that there is any one best practice. It could be by individual analyst, or by team, or by project, or by report name, or anything else that you think of.
We have about the same set up? Do you also keep the data sources from extracts in your off-line repository. 10gb will fill up quick. I tell my folks after they've published they can delete these. If they need to get back to the workbook, they can re-extract if necessary.
Just a thought.