I am running Ubuntu in console mode. Do I need console-kit-daemon to be started? What is it doing? Why is it necessary? Can I turn it off? How can I turn it off? And so on...
No. ConsoleKit only manages console logins in graphical mode, so if you're not running X or a desktop environment it's OK to turn it off.
Here's a comment from this question showing how to disable console-kit-daemon:
Hope this answers your question.