Chinese input I'm not sure

but you might want to try SwiftKey if they support Chinese input or not.
Backing up TA is done once but recommended you back up additional by copy-paste the backed up folder/files, or upload a copy to Cloud service.
yes, firmware update, just wait for NUT or whoever that is handling the root to upload the flashable firmware. recommended not to use OTA or PC Companion because it might delete your root.
the only reason why you're not able to update via OTA or PC Companion is because
1) TA partition does not exist (it's like a license, unique and not able to use other phones')
2) Bootloader unlocked
3) system/app modified
TA partition only goes missing when you unlock bootloader, which is why you need to back up, then restore it after unlocking BL.
okay, get it.. thanks for your help