I think I'd rather recommend Diana Wynne Jones' The Tough Guide To Fantasyland. On one hand, it's more conventional modern genre fantasy derivative of post-Tolkien writers. On the other, it's an actual survival guide, like the OP.

"Gawain" is an example of the source material from which a survival guide could be inferred.

I recently learned that Tolkien's son did some cleanup on the various writings left around after the passing of JRRT. (the phrase was, nothing was added, only removal of any contradictory passages and order). Any tips for finding more of Tolkien's writings, Middle Earth or otherwise?

I don’t have time to right a proper reply right now (May try later) but the real situation is really complicated. Tolkien spent his entire life writing about Middle Earth and the Lord of the Rings is only a small part of his output. He also wrote academic output and some other stories. Tolkien himself sometimes wrote different versions of the same tales, sometimes in different styles, often making changes to the characters or plot points. He had no version control. After his death, Tolkien’s son Christopher pulled together The Silmarillian, which is a précis of some of the key stories of the Elder days of Middle Earth. He then published, over several years, books that presented some of the raw material, explicitly pointing out Tolkien’s own contradictions and retcons. This can be fascinating but frustrating, especially when Tolkien abandoned good stories and characters midway.

library search, probably.

lesser-known gems i like are his translations ( of gawain, pearl, and sir orfeo), his critical essays (monsters and critics), and his short stories (smith of wooton major, farmer giles of ham).