Do's and don'ts when writing an academic book

I am currently writing a book in mathematics. I have written a few pages and often stumble upon the question "is this good pedagogy" or is this "good typography". The chances of my work getting published is slim, but I am using it for a personal collection of notes and ideas in addition to learning writing a longer text. Below is an excerpt from my notes

An older version of my notes can be found here.As now the notes are dividied into a somewhat strict pattern with lemmas, propositions, corollary with theorems reserved for the main purpose of each section. I have a ton of questions about layout, design how formal to be in my writing, and how spiced up I should make the text. I see modern calculus books like to divide the text into blocks (a different color for theorems, proofs etc) while published articles tend to keep a much more minimalistic presence. I just do not know if I am on a good path, or if I need to do some fundamental changes.

To summarize

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  What are the do's and dont when writing longer notes (mainly aimed at undergrads).

  
  


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  Are there any books or literature on writing longer academic texts?