Flash Backup and Revert to stock Archer c7 v5 US

I have an Archer C7 v5 US version, and it is currently on latest stock firmware 1.0.15 Build 20200628 rel.63501(5553)

How can I backup my original firmware so that I can restore it easily through tftp if and when things go wrong, like the cases where a stripped firmware is to be used to recover it. I could not find a stripped stock firmware for the v5, and the wiki has one for the v2, and the instructions doesn't seem to work for v5, as per some users' comments on this forum.

How do I perform a backup before installing openwrt?

If I flash openwrt through tftp for the first time, will it mess up the flash partition?