I've found that 16-32GB is the sweet spot for flash/thumb drives as anything larger is a waste of money. If I need more then 32GB for a single file, then it's time to break out the external 2+ TB drive.
The main advantage is that 16GB are cheap and work well for Sneakernet file transfers
I'm going to chime in on this. From what you've said, what you want is a Backblaze 45 drive storage pod. This isn't going to be cheap but with the right setup, you now have an easy to update Storage Server - you'd need two of them and mirror the two offices.