Thanks! Feels like it's all coming together.1. If you format with SPFT and don't have IMEI backup you'll lose all the keys of your device. Make a backup first. After flashing stock, unlock bootloader, flash twrp.
3. No. You need to restore data to vendor partition after you deleted it's data, this is where all the drivers are. Para is a partition that holds a flag that will prevent booting even on a working system after a bootloop. You need to restore it to be able to boot.
4. You don't need permissiver, but of course you need to flash disable verity and optional encrypt, encryption is not supported in TWRP and GSI's and verity needs to be disabled to be able to boot any custom ROM.
Two last questions: "If you format with SPFT and don't have IMEI backup you'll lose all the keys of your device."
1. is this a different back up than the vendor/para back up to be done in twrp?
2. what "keys" are you referring to?
Because I've already semi-bricked my device many times, each time I just flash back to OEM with SPFT and it works. Should I be worried about this?