1. Yes, I check if the device has custom ROM support and rooting, at this point I can't use stock ROM, be it any device if it supports Bootloader unlocking or tinkering , I will do that
2. I'm using Redmi K20 Pro with MIUI EU 10 installed.
3. Gonna use it until it dies
4. Xiaomi stopped support and performance took a big hit, with upcoming updates like 12, 12.5 device performance degraded a lot , tried many Roms but Battery Backup was hit or miss , so downgraded to miui EU 10.