"i assume you know this, but I'll link if you need more background or refresher".
You're almost right is here :) Actually I put many links and not give much explanation only with one reason: kernel is very very big code-base and it is very hard to explain every line of code
Yes i know abot this blog, really great artucles. Reading and trying to understand linux kernel source code too and planing to write series of blog posts about it after assembly
[author :)] I'm not sure that i can recomend somethig for you, but for things that i use for learning low-level programming are following.
1. Nasm manual
2. Intel manuals
3. gdb
4. Source code written by other peoples, like bootloaders, simple 64 bit operating systems and etc...
Maybe for understanding how computer works? What occurs when you launch program, what occurs between turning on computer and that moment when you see login screen, what is it printf("Hello world") and etc... Many interesting questions. Of corse assembly is not answer on all questions but the way to it