Alec,
The best way to learn Nodebox is to do just what you are doing: play, make things, then browse through the forum to learn more.
You are not the first person to wish for better annotation tools. I'm afraid there's not much there. You can add a comment to any node that appears when you hover over it, but that's about it. One other trick is to make a string node, holding any comment you wish, and then place it near a cluster of other nodes. You can turn such a node bright green so that it will stand out a bit more.
As for compressed output, Nodebox is purely a vector tool. So when it exports SVGs or PDFs it only outputs the pure mathematical description of the objects, which tends to keep things compact. For vector output the canvas dimensions don't matter much, since it will render perfectly at any size.
When you export PNGs or MP4s then the canvas size does matter, since Nodebox converts its vectors to raster. But even then, output often consists of object outlines with negative space behind it which often keeps file size fairly reasonable. If you use my image node, though, to make pictures with simulated pixels, file sizes can balloon quickly.
Your foo_fighters animation is simple but intriguing. It's true that you could make the same thing with fewer nodes, but that will come with experience.
When you search the forum you will soon come across my Cartan Node Library:
https://forum.nodebox.net/t/8423098352/cartan-node-library-3-6
There are now almost 200 nodes in the library, each with a demo, all free for use with no restrictions. Just copy paste them into your own projects. There's a lot to absorb there, so don't try to understand it all at once. Just browse, grab whatever interests you, and play with it.
Nodebox is no longer under active development, but it's open source and we are free to add and share our own nodes (actually subnetworks), as I continue to do. Nodebox is also extensible: you can add Python or Clojure code libraries.
I've been pushing the boundaries with Nodebox for over ten years now and the possibilities continue to expand to the horizon.
John