Here is a video to demonstrate what I can do with the rig so far.
It mostly works well, but it does have one problem, which is in the left upper-arm and happens only when I try to use the back control.
When I move the back control, the upper arm collapses and the forearm just stays in its place; in contrast to the right arm, which moves perfectly. I have tried several solutions, such as using the component editor to either increase or remove influence from the shoulder or the forearm and also painting and removing weights, but none of these seem to work. I have also tried reconstructing the controls in the left arm from scratch but this also does not work.
If I manage to find a solution to fixing this problem, I will post it up here.