Very cool stuff!

Only nitpick I'd have is that author decided to use a custom-design cpu.

Ok, "discrete logic only!" is a valid choice. And then keeping complexity to a minimum weighs heavily. But the downsides of that choice are also considerable:

-No interrupts (which are very useful)

-No existing software base to tap from. Somewhat-useful C compiler helps.. somewhat.

But who am I to question author's choices for a hobby project like this? Great stuff in any case.