Thank you for your question, Fred.
Though I do not doubt our braille-using friends, students, and neighbors would make sense of contracted comments within a numeric passage, I cannot recommend it.
A numeric passage indicator sets grade 1 mode until the numeric terminator ends that grade 1 mode (RUEB2024 §6.9.1). If we use contracted braille within a numeric passage, then we use symbols that have a grade 1 meaning in an environment that says their grade 1 meaning is what’s important.
In responses to your questions:
Q: Yes, everything within a numeric passage is in grade 1.
1) A math comment like 300×32, would be brailled without the numeric indicators within a numeric passage.
2) No. For the sake of clarity, translatability, and consistency, we should not braille text comments contracted within a numeric passage.
Regarding your key for comments: I really like your placements of the key letters (i.e., each following the quotient piece to which it applies). However, remember what RUEB2024 § says: “… any lowercase letter a-j is preceded by a grade 1 indicator.” Since you’ll have to use a grade 1 symbol indicator for each of those letters, I think you should get rid of the periods. Also, in your key listing, please check the formation (and grade 1 indicating) of your letters (especially the b). One more note: you do not need a blank line before the braille line that contains only a numeric terminator (GTM §4.1, last paragraph before 4.1.1).
In other words, regarding your #3, it is a good choice to use a key for the comments, and it seems practical to use a TN to explain the printed down arrows showing numbers in the dividend moving.
Last, but not least, I agree, spatial division with operation signs is challenging; I think you’ve done a very good job of aligning by place value and placing the symbols of operation where they apply.
Braille on!
–Kyle