Been doing some of this demon rig, very hard, very annoying but learning a lot, Fun though.
Basically started with laying out some markers so I could place the bones in the exact positions.
My first bones down, the arms and legs, everything is orientated to make sure its all in the same direction and theres no rotation in the bones.
Fingers were tricky as the models hands are curled, but using the marker trick I have managed to place the bones in the correct place.
Everything Aligned and orientated, first bones in.