I agree with Chris here in that your aim should be to get the rig as neutral and longitudinally balanced as possible. Keep notes on what you need for each different configuration of lenses, focus lights etc.
I would follow up on the contract but also nurture the relationship. Being paid is a good step that many dream of, especially from a entity such as the BBC. I agree with Mike regarding the details but it's a good first step. Obviously you have something good there.
If I can throw my tuppence worth into the hat? It seems that half the struggle with settings you are experiencing is due to you attempting both natural light video and flash photography on the same dive.
Two different beasts both competing for your attention. Different settings mean you spend a lot of time switching between the two rather than focusing on one discipline.