We currently don't put a limit on how much data you can store in each of your groups.
Why? Many users keep their documents on Google Drive or Office365, but like to have the easy access from SquidHub. Therefore, they add links instead of uploading the actual files to SquidHub - which is the very reason why we can currently offer you unlimited storage.
Read more about how to link to documents on Office365, Dropbox and Google Drive.