Keep in mind unlocking your bootloader will most likely wipe your device (security reasons), so back anything up beforehand.
Installing a custom ROM is optional, as you can have stock-rooted by just installing a custom recovery and flashing the SuperSU zip through recovery to install the su binaries.
Installing a custom ROM is optional, as you can have stock-rooted by just installing a custom recovery and flashing the SuperSU zip through recovery to install the su binaries.