OK.. then you cannot fix yourself. EDL and you need authorized account to fix.
Regarding the message, hold power button for 20 seconds, this will reboot EDL.
Well there are other ones, you don't need root but some needs permissions set with adb to show all other process and sys apps. I use GSam battery monitor, all you need to do to have all other apps is to give it BATTERY_STATS permission.
Correct. But there is WIP on TWRP for A12 for venus ;)
( It is not mine and it will be available public once the devel feels is ready, but for me it is already better than the hacked Chinese one )