n28690: add notes and questions

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Thanks a lot for helping with my understanding of our build system as I was prepping for this @hebasto and @thecharlatan . Would greatly appreciate if you could have a look at this and lmk if you see any inaccuracies or room for improvement!

At the moment, I'm leaning towards doing this as a single review club, since I think the concepts are much more important than the code changes here (which is largely shuffling things around). Although it may be worthwhile to dive deeper into 1f98ed5e56230a61b699f669459e39fa101a1ca5 too, depending on feedback?

[stickies-v]

Thank you for the review @glozow, addressed all your comments. Discussing this with @hebasto and then RFM later today.