The box provides apr. 120GB storage capacity, which should be enough for first steps, mails and some files. If the space is getting small you may add USB storage or shares from you NAS-Device (Synology, MyBook, QNAP...).
Just move some or all objects (calendars, email addresses, file shares) onto the new storage locations during normal work.
Just mark space on your NAS-Devices or USB drives as back up drive. All files from the choosen objects are transferred onto the back up medium. Optional you may create an archive where up to 30 different versions (from daily up to 10 years) are stored additional.
Please keep in mind that a reliable back up requires multiple usb drives, which are connected at different times. A backup to a NAS devices requires an additional copy on an offline medium (to be protected against burglars, fire, over voltage, viruses).