WLaC is also good, because it describes the role of Capital itself within Capitalism as it relates to Workers, and thus allows Capitalists to exploit them.

CotGP is added because it clears up a ton of misconceptions people who have not read Marx yet consider themselves leftists have about Marx and what he advocated for, practically. He essentially dismantles a weak Socialist/Social Democrat plan and explains the transition to Communism. He even adds on just how lengthy a process reaching higher-stage Communism will be.

Edit for your edit:

Yep, it's always cool to see logical analysis lead to correct conclusions that later make themselves apparent. It's funny how often Marx ended up being correct even on limited information simply due to strong analysis.