> I am hereby officially integrating 'bandwidth' into my tech vocabulary, ...
It was easy for us to remember, we associated the term with the hip party of our instructor.
> how much bandwidth the average Moodle user needs on an average
I don't think this is Moodle-specific. If the user has a 1 MBit/s line, he is used to that speed and expects the same from the Moodle server.
So you can reverse the question: If the server has a 100 MBit/s upload speed, it can serve 100 users, each consuming 1 MBit/s download - provided 'fcourse that the machine itself can deliver that much!