Short answers, pulled from the story.
Splinter of the Mind's Eye is a 1978 science fiction novel by Alan Dean Foster, published by Del Rey, a division of Ballantine Books. It is a sequel to the 1977 film Star Wars and was the first full-length Star Wars novel with an original storyline released after the film.
Han Solo was excluded from the novel because Harrison Ford had not signed a contract to appear in any Star Wars sequels at the time Foster's contract was drawn up. The book was conceived as a low-budget filmable sequel, so the cast was kept small.
The Kaiburr crystal is an object in the novel that focuses and amplifies a user's connection to the Force. A fragment of it, carried by a character named Halla, drives the plot of the book, and the full crystal is found at the Temple of Pomojema on Mimban.
No. When Star Wars broke box office records, the planned film adaptation of Splinter of the Mind's Eye was abandoned in favor of a big-budget sequel that became The Empire Strikes Back. The novel had been written specifically as a contingency if the original film was not successful enough to fund a large-scale follow-up.
No. After The Walt Disney Company acquired Lucasfilm in 2012, most licensed Star Wars novels and comics produced since 1977 were reclassified as Legends and declared non-canon in April 2014.
Mimban appeared as a planet in Solo: A Star Wars Story in 2018, and concept art for Rogue One in 2016 used the name Mimban for a location that eventually became Jedha in that film. Marvel Comics' The Rise of Kylo Ren also sent Ben Solo to Mimban, where he encounters an object possibly linked to the Kaiburr crystal.