Plane geometry: high school mathematics is enough, as above;
Electricity: Same as above. If you want to know more, you can look at Circuit published by Tsinghua Publishing House.
Personal opinion, step by step, first look at the third grade students who are watching high school. Only with a solid foundation can we understand more advanced knowledge well, otherwise it will be a waste of time and energy. By the way, be sure to add enough math knowledge, both of which are indispensable.
Mechanical quantum theory, you mean mechanics and quantum theory, or quantum mechanics?
Mechanics: After reading Grade Three and Grade Three, we will look at theoretical mechanics, or analytical mechanics, material mechanics, structural mechanics and so on. And there are more than a dozen common courses, which are very detailed, depending on your preference; But if you really want to see it, I suggest learning math first, and have a good foundation in math.
Quantum physics or quantum mechanics: in the second day of junior high school, it is really not recommended to read textbooks, and it is more appropriate to read popular science; Step by step, lay a solid foundation for basic knowledge, but still do not understand enough. It's good to read Hawking's A Brief History of Time and the Universe in the Shell. To tell the truth, classic popular science books are not a blow to you, but you really can't understand them. But the advantage of such books is that even if you can't fully understand them, you can always broaden your horizons and inspire your thinking. Reading them several times will definitely benefit you a lot.
Hardware: University textbooks are called Computer Hardware Fundamentals, or some are called 80x86.