As an amateur stair builder, of about a dozen stairs over the course of many years, a few remarks:

As a youth, had the wind knocked out by a super steep, narrow tread stair. The rise and the run are important. Building codes apply. A rise of about 7 inches comes to mind. The run should be enough to accommodate the foot. Circular stairs can easily have too narrow a tread width on one side. (Historically, Right hand screw for sword defense.).

It is easy to mess up the rise for the first and last tread.

So triple check your math!

Railings should be continous, and/or not trap the hand, or other body part.
If a section of the stairs is straight, with extra wide outer curved section, the two slopes may well be of different slopes, and also the railing

Check out Google searches.

- Brian

There are also rules about 4 inch balls not passing through stiles, balusters/ spindles. (Baby's head, etc)

Engineer should design. And building Inspector approve...

So yes, I am hung up on safety.