I wouldn’t agree with what you said about assembly peter. Its still very useful when you’re wanting to do things like complex rendering, but its quite hard and not many people have those good skills in low level programming for it.
As for OpenGL and DirectX. OpenGL is easier to learn but is harder to do harder things in. DirectX is hard to start with, but easier to do harder things with.
Yup, physics with balls is always a good starting point. Something nice and simple. Get it working properly and then, if you’re feeling ambitious expand it, don’t get ambitious at the start, always get the basics in first!