[ZTE Axon 7 ROMs, Kernels, Recoveries, & Other Deve] Oki:
No problem mate.

This guide should work. If you specifically want to use the backup of that version, then add two steps:

1. flash TWRP 3.2.1

2. Reboot to recovery and restore your backup.

This guide should work.

No, TWRP Labs Mod is a recovery, it won't format or overwrite any partition other than your previous recovery. IntSD is wiped only when you format your userdata partition. That happens when you add or remove the vendor partition in front of the userdata partition, or when changing the filesystem between ext4/f2fs.

TWRP Labs Mod is able to restore the official backups. NFound versions use a different folder to store the TWRP backups. All you have to do is to move the NFound's TWRP backup folder to the official location, which is a folder with the ID of your device inside /external_sd/TWRP/BACKUPS.

There is always a risk of having a complete brick if you do not take the correct measures. For your safety and peace of mind, I always recommend the use of a Bootstack supporting the EDL boot by using the VolUp+VolDn+Power combo. The EDL Backup creates ZIP files that can be either be flashed like any other TWRP zip file or by extracting the contents in your PC and flash them using MiFlash or any other similar tool. So there is no risk as long as you can boot to EDL and have an EMERGENCY EDL backup on hand.

You have to remove the vendor when going back to stock. Just run the PARTY tool and remove it if you have it in your system. No need to wipe it.

The easiest way to do that is by flashing the EDL package from a computer. However you can always remove the vendor partition and flash any backup ZIP of the stock system.

Flash the EDL package for the stock ROM and relock the bootloader. There are some guides for doing that. TWRP don't help on that. No matter what you need a pc for unlock and relock.

PARTY can create 2 different sizes in 4 locations of the eMMC. The recommended one is the end of the system partition. This way there is no need to reformat the Data and intSD, vendor can be added and removed on the go, and the host partition can be hot resized without losing any content, in other words, the files inside the partitions remain untouched.

The FULL EDL backup doesn't have any personal, or device data such as IMEI, SN, MAC, etc... so you can share it with everyone. Only EMERGENCY and ALL options include device specific partitions.

There is no need to do that. LOS bootstack is actually a B12 bootstack. The risk is the lack of EDL boot support using the button combo. The Bootstack linked in question 5 is compatible with all LOS and NFound ROMs and include EDL boot key combo.

It is up to you. MINIMAL allows you to boot recovery and flash anything. FULL includes also an OS. Probably EMERGENCY+FULL, or MINIMAL+ALL could provide cover for any situation.

The Bootloader unlocked message removal works with B32, B10 and B12 bootstacks.

The standard recommendation: do NEVER flash, wipe, create or delete without a complete backup of your device and a bootstack with EDL key combo support. If you are covered, then you are safe.

Yes, you can. Just flash the other version and reboot to recovery. I was even thinking in integrating a dual kernel boot, switching from one to the other with the press of a button to trigger the swap and the recovery reboot. This is one of the improvement projects.

PARTY allows that, but having the vendor next to system allows for a quick on/off of the vendor partition, and then there is no need to reformat anything. Adding the vendor using data as the host partition can affect the userdata and makes things more complicated.

An EDL backup can be restored with any TWRP regardless of the bootstack or TWRP version. Or flashed from the PC using MiFlash.