If you don't mind working with software emulation, nand2tetris takes you from logic gates up to a CPU, assembler, compiler. I'm working through the book: https://www.nand2tetris.org/book. It doesn't focus on an existing architecture like 6502 but focuses on simplicity instead to make the ideas really clear.

If you'd like to work with real hardware, +1 to the Ben Eater suggestion. He sells kits for all the components for an 6502 machine so you don't get bogged down in sourcing them. Great videos too.

(Quick edit, not 8086, showing my inexperience with hardware!)