So far the most useful documentation was at Lineage's Redmi section, random "mobile enthusiast" sites were "not very good" and youtube videos are to be avoided like the plague.
- SDK platform tools from android.com
- mi flash unlock gui tool (
miflash_unlock-en-5.5.224.24.zip
) - newest twrp for device (
twrp-3.5.2_9-0-santoni.img
), from twrp site