1. Yes. Force basic key attestation.
2. Yes
3. https://xiaomi.eu/community/threads/the-ultimate-guide-to-unlock-bootloader-use-twrp-flash-beta-from-stock-rom-setup-and-hide-magisk-for-mi-10-umi-plus-extra-tips.59306/
Theres good instructions. You have to do full wipe if you go from A10 to A11.