So if there's 18000k words that's slightly under 2/5ths of a novel (50,000+ words). I'll say right now that by 1/5th in, I'm ususally getting into some meat and potatoes. (Hell, my novels are broken into short stories with the same principal characters and several events acting in a serial fashion from chapter to chapter. 10,000 words is easily decently sized story, but I've gone higher than that).
I would approach this like "Star Wars" in that the first six films started as the plot for 1 film, but Lucas rightly realized there was too much going on and decided to put out a snippet of the story to get the idea across. In a modern setting, there are three schools of thought as to how to properly watch these films for the first time to get the best of the story (Name in quotes is by me): Chronological Release Order (Watch in order IV, V, VI, I, II, III), The "Tradgedy of Anikan Skywalker" order (Watch in order I, II, III, IV, V, VI), and the "Epic of Luke Skywalker" order (Watch in Order, IV, V, I*, II, III, VI).
In the Chronilogical order, the two trilogies are taken seperate stories in the same verse with the original version where Luke is the Protaganist and the prequel where Anikan is the Protaganist. This preserves how audiences were first introduced to Star Wars in real life and allows a first time watcher to have the same questions and answers.
In "Tradgedy" order, it fixes Anikan as a protaganist going through a fall and redemption arc and follows him from a wide-eyed idealist with romantic notions about life outside of Tatooine, to the hubris of wishing to saving people who are important to him causing his descent into Darkness, until he is at war with his own son. It means that Vader's actions in VI in siding with Luke show that he now understands what he did wrong in III and counters his selfish acts in the latter with selfless acts in the former.
In "Epic" order, Luke is the Protaganist, Anikan the Antagonist, both are human and both are very much a like in that the ultimate moment of their final two chapters shows that they are facing a similar thematic choice: Loyalty to Family vs. Loyalty to a cause they believe in. Love is contrasted with desire for power, as Anikan's desire to control that which he could not is shown in counterpoint by Luke's rejection of selfish desires for a greater good.
I bring these points up to show that it's not a bad thing to show that the setting of your story is a lot more than just what is intended to be seen in the book. Star Wars is almost 40 years old and runs on the notion that every extra has a story to tell giving the whole setting a very grand and lived in feeling. It's not a bad thing to give your readers more... but you need to ask "what is the story I want to tell first." And then look for what is the most thematically important aspect to that story (and maybe tease the rest in subtle mysteries).
- When I was originally was introduced to Epic Luke order, Episode I was omitted or told to append to the end if your new watcher wanted more Star Wars. However, David Filoni's (One of the producers on Mandolorian) comments in the making of series have caused me to greatly re-evaluate the importance of Episode I in Star Wars, and has largely given me a critical lens that redeems it out right (I still make Jar Jar jokes, but half the fun of Jar Jar is laughing at/with him. He a lovable loser to me.).