Ok, so I’m starting all over with my beginner biped triple limb rigging ( for FK / IK switching).
I have the base skeleton built with correct LRAs. I duplicated the arm and leg
chains twice and snapped them on top of the base chains. I’ve heard from 2 other
members that say I should parent constrain the skeletons together first before I add any
FK or IK controllers. Is this correct ? if not, how would you do it ?
I did try adding controllers first, but I ran into problems.
hmm, it’s not correct, but it isn’t incorrect. 
The order you constrain things shouldn’t strictly matter, unless the act of constraining changes the transforms of the object, or if it changes the inputs of the next operation in your process. If the inputs of your step are the same, the order doesn’t typically matter.
What I would do is explain the problem you ran into. Errors or unintended behaviours. And then work back from there. What happened?
Yes that does make sense about the ordering. I had a problem when hooking up the
knee pole vector, it offset the chains. But if I snapped the pivot of the PV controller to the knee
joint, the chains lined up again. We actually have talked before about this
and this is what you wrote:
The order of operations isn’t so important. But if you want to avoid that offset, you need to calculate a position for the polevector control that is exactly lined up with your IK joint triangle. (And also make sure your joint orientations are clean .)
That same calculation will be used if you ever want to do seamless IK/FK switching with a script.
Here is a Pymel script I wrote that I use. https://gist.github.com/chris-lesage/0fcc9a344f2096cf6c82a353cb735b3e