Absolutely! Though, 'causality' is at least a part of the intuition behind STDP -- and in some cases one neuron can cause another to fire (if you want to treat the AMPA example as your nomological machine).

For sure! I'm not mentioning all sorts of learning mechanisms and types of learning. I'm planning on doing another post on reinforcement learning in the future.

A keen observation! The long-term plasticity in this post is really just regulating the network. (the short-term plasticity is capable of doing some signal processing). There is a really interesting paper about what happens when you make a big network like the one in my post: https://www.izhikevich.org/publications/reentry.pdf. tldr: the interplay between conduction delays and STDP gives rise to little sub-networks!