A: The A37m hardware supports GSM/HSPA/LTE. Yes. After flashing Global firmware, the radio bands unlock to standard international frequencies.
A: The A37m does not have a user-unlockable bootloader like Pixel or OnePlus. Flashing via EDL does not touch the secure boot. You are safe.
Disclaimer: This guide is for educational purposes. Manufacturer warranties are voided by unofficial flashing. The author is not responsible for bricked devices.