So basically I sucked at the component diagrams, that's where I lost most of the marks. I thought I had everything OK, my solution was fairly standard I thought. However I think my submission just had too much stuff in it, I think I went a bit overboard.
Another thing I think might be relevant (but since there's no feedback, who knows?) is that I largely fudged the issue of integration of FF system due to what I took as incomplete/contradictory requirements.