This seems the wrong way up to me, in that a CPU from scratch seems like a much ...

This seems the wrong way up to me, in that a CPU from scratch seems like a much harder thing to achieve and learn from. But I'll agree that the "analogue" build a circuit stuff is very different to the digital stuff.

> 555 timer

Very much an all-analogue part; possibly easier to understand in its non-integrated version: https://shop.evilmadscientist.com/productsmenu/tinykitlist/6...