It seems like that bootloader has been locked. Go to faatboot mode and check with miunlock. It should unlock the phone and will work normally.
Sent from my Redmi Note 3 using Tapatalk
No xiaomi.eu roms as of now.
For covers and protectors, all note 3 have same dimensions and cuts so no issues there
Sent from my Redmi Note 3 using Tapatalk
Yes. Sometimes it take about a week to sync the unlock permissions with your account though you got confirmation. Mine finally passed 50% after 12 days. So if you just got unlock confirmation, better wait 1-2 weeks