Hi Shadow, thanks for the feedback.
I actually discuss the xray feature in the section on setting up the reference images. You are right about using the default cube would have probably been easier. Thing is, the very first thing I do when I install Blender is erase the default content ( cube/light/camera ) and save preferences.
You are absolutely right about the mirror modifier not using the 3D cursor, but I've found the modifier extremely problematic if not done about the origin, it might be overkill, but it works consistently. Otherwise it just seems to be somewhat buggy. I should note in the comments that this isn't required, ditto about the clipping ( oops ). I've updated the tutorial accordingly.