Is there a nice resource somewhere where one could endeavor to learn about how LaTeX works internally? Because all those tricks look like they follow some internal logic that I am entirely unfamiliar with.

I haven't looked at it in some decades, but Knuth's original TeX book was surprisingly readable and informative.

Those who endeavor to understand the inner workings of the LaTeX codebase only have pain and suffering awaiting them.

For example, http://latex-project.org/svnroot/experimental/trunk/l3kernel... or even http://latex-project.org/svnroot/experimental/trunk/l3kernel...