I was told to set Read Only Access that the user is assigned 0 MB storage space. However the minimum Storage Space that can be set is 5MB.
How do I set Read Only Access for a user?

thanks.

By default, DriveHQ creates some sample files for each user. You can delete these files / folders before you can set a lower storage for your sub-users.

With only 5MB available space, your sub-users cannot really upload anything meaningful to their own account. So they should only access your folders through the "DriveHQ Share" folder.