If it's crashing at startup, it might be due to the network SMB device scan. Try disabling your wifi on your Quest headset, then launch HereSphere. If it doesn't crash, go to the user settings, and disable the "Network SMB Device Scan" toggle. You can then re-enable your wifi.
The "save backup" button in the HereSphere user settings saves it to the root folder of your Quest local storage under the folder "HereSphere". Not sure how having multiple accounts on the same headset affects this, as I haven't tested with multiple accounts.