Balancing coursework, research, and teaching
I think the answer lies in what your PI thinks you should be doing and how well you can, at least, appear to be doing it while doing things other than research.  Even if your PI doesn't enforce a certain allocation it's in your interest to do as much research and little else as possible. You won't get a PhD by teaching or taking classes. An overload, in my experience, is unavoidable first year. Is is possible to take electives that your PI teaches? That's about the only coursework he or she won't begrudge you.