My degree is in Applied Math & Computer Science, at an engineering school, but the CS aspect was rather lame and the applied math part was basically useless for

My degree is in Applied Math & Computer Science, at an engineering school, but the CS aspect was rather lame and the applied math part was basically useless for computers. But I got the piece of paper, which was my main goal. So like you, I've taught myself pretty much everything I know about computers. You mentioned reading a book on Postgres. If you don't know SQL, I'd recommend learning that, either with Postgres or maybe more simply with SQLite. Whatever you pick as a toy project, make sure it has lots of data to help you understand indexes. With small data, everything will be fast. With large data, like a few million rows, you have to become very familiar with how the database actually executes queries so you can add the correct indexes to make things run fast. And you can't just add indexes for every query, because that slows down inserts and updates; there's a trade-off there that you'll have to balance.