ALWAYS use a custom Django user model when starting a project. This is one of the best up-front investments of time that I know of in creating Django projects. Every time I haven't taken the time to do this the right way up front, I have regretted it. Every. Time.
Most of us have had the experience of loving a CMS at first, but souring over time, as the limitations and shortcomings come to light. We have had this experience too many times during our careers, as both users and developers of content management systems. What if something better could be built, which would withstand the test of time, and still be loved after years?