Comment by WillAdams

I've been trying to make this sort of thing more tractable by modeling the movement of tooling in a CNC machine so as to make 3D parts using Python in OpenSCAD (https://pythonscad.org/):

https://github.com/WillAdams/gcodepreview

That said, the only 3D CAD tool where I was able to follow the tutorial (after a fashion) was Dune 3D: https://dune3d.org/ --- if you haven't tried that, I'd highly recommend it.

The usual way to get started w/ molding is to make a vacuum molding machine:

https://makezine.com/projects/diy-injection-molding

(I remember one such plan page where the first project was to make a handle to make the machine more comfortable to use...)