In that case you may try the LineageOS+MicroG version 
This version works without google apps.
And to get really google-free, have a look at /e/ 
TWRP backup the system, not the “internal storage” (media/sdcard0), for this one you could do normal copy and paste after connecting to your PC (with MTP/ file transfer option). However, when you charge a TWRP backup this internal storage is not lost ! So no need to backup it every time, except for a full wipe! 