fantastic list! although obviously no such plan can really cover the whole space, i cant help but want to suggest adding some languages representation to the list; a simple interpreter or compiler project, or alternatively some symbolic computation eg algebra or differential calculus. being exposed to this stuff via Racket was hugely transformative for me (e.g. https://beautifulracket.com/stacker/why-make-languages.html), but if lisps arent your thing theres plenty of great projects in e.g. java as well: https://craftinginterpreters.com/contents.html