Whoops, I didn’t notice the questions here…
walshlg - for your first question, I’m not entirely sure why to use ‘average value’, haven’t been able to find much info on this subject, hopefully documentation will get written for this. I know ‘scripted expression’ is for python expressions. But I do not know the difference between average, sum, minimum, & maximum.
To use this setup in animation, you would keyframe the location of the controller bone since it’s location controls the shapekey.
Yes, the armature is just sitting there. In practice I would parent the graphics (the box around the control bone) and the control bones to the ‘master’ or main bone in the rig. This way it would all be 1 armature. You can use 2 armatures on the same object, but I avoid this to avoid confusing myself…hahaha
As to creating separate actions for the body and the face, that would just be a matter of personal preference. You could create separate actions for face & body then combine them in the NLA editor. You could also create one action and if you want to adjust say the timing of the facial part of the animation, you can select those keyframes in the dopesheet and adjust them from there.
As to the ‘why’ behind equations this allows you to adjust how the controller does it’s job. The example in the video tute shows the mouth open and close based on how much the controller bone is move with 0 movement = 0 shapekey, movement of 1 blender unit = 1 shapekey, or fully on. Let’s say I want the shapekey to be fully on if I move the controller 3 blender units, then you would adjust the equation to achieve this.