All Z2s come with the bootloader locked, so yours will be locked.
The unlock and root procedure in the OP does NOT require root, so you can accomplish it as soon as you get your phone and have an unlocked, rooted phone. The warning is that you will not be able to do a TA backup (which is NOT necessary to complete the unlock and root procedure described) if you don't have root already, so you will lose your DRM keys which are needed for some special functions on the Z2. You may or may not care about the special functions.
Im not familiar with Sony's rooting routine. What exactly are the TA backup and the DRM Keys?