A quick way (automated) to symmetrize the left part of the rig to the right is using the Specials menu in the Edit Mode of the Armatur.
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Select the Left side bones
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Press “W” -> Symmetrize
This automatically duplicates and mirrors all the bones in the selected axis Tools Bar, it also automatically switches the names of the bones from _L to _R.
However, I did have some issues regarding the IK constraints, it seems to be inverting the orientation of the bones somehow (Roll angle * (-1)).
