Or you could go from an even more fundamental level with a simple course https://www.nand2tetris.org/ https://www.nand2tetris.org/ You build up a computer from

Or you could go from an even more fundamental level with a simple course https://www.nand2tetris.org/ https://www.nand2tetris.org/ You build up a computer from simulated logic gates, constructing the ALU, CPU, Ram, I/O etc. The opcodes are comparable to those in the CPUs you mentioned, but you have the added benefit of the magic that occurs when it is able to process those opcodes. The best part is, thanks to the courses exceptional guidance and streamlining, it only takes about half a day or so to get it to that point. After that you can follow the rest of the course to making a compiler, etc. Or you could move to an NES emulator as you mentioned. The nand2tetris halfway mark would also be a good jumping point for the principles, compiler, and RISC equipment mentioned in the OP's course.