Regarding your question, USB storage used to handle the downloaded data, but now it is for your personal storage. From the Skylark v1.0 User Manual at https://github.com/Outernet-Project/Information/wiki/Skylark-v1.0-User-Manual (Outernet forgot to change the manual's name to v1.2)
Adding External Storage
External storage may be used to add other data archives, to be used over the UI. Use of external storage to increase the available storage for downloads is no longer supported.
The device may be formatted using one of the filesystem formats: FAT32, and Ext2, Ext3, and Ext4 on Linux).
I have found it very useful to use with a 64 GB USB stick that holds the entire 32 GB Rachel database found at https://racheloffline.org/