Older devices are harder to bootloader unlock, but nowadays they make it easier. My Verizon Note 3's unlocked too. The carrier usually makes it harder.
Farewell to John Warnock, an internet pioneer and co-inventor of the PDF whose invention actually made the world better
I literally reinstalled Windows the other day and systemd-boot was still working, and so was Windows. This is all on a single disk.
Backup your home directory to a separate drove, then wipe the drive and create separate partitions for /, /home, and optionally, /var.
But don't use those, they're vastly inferior.