Properly backing up Android phones is still a mess nowadays. Perhaps, you can go the “Upload everything to the Google Cloud” way, but I have no experience on it and it is bad from a privacy perspective. Besides, you will not be able to restore your backup on /e/. My thoughts:
- If your bootloader is unlocked, you can make full system backups (so called “nandroid” backups) using TWRP. This will help you to go back to normal if something fails.
- Internal storage can be backed up by dragging the files to your computer.
- Many apps have their own backup mechanisms (e.g. “export settings” or cloud backup).
Edited including @AnotherElk’s remarks.