Per your request, I will attempt to shed wisdom on something which I'm still discovering for myself, namely, how long should a novel be? How many words? I don't have a specific number I'm adhering to in my novels, rather, a certain feeling I have gathered from reading books, primarily traditionally published. I would imagine this topic is more of a pressing issue for self-publishing authors as we have no team of professionals to rely on, somebody who can tell us how long our novels should be, depending on the genre, on the type of novel, etc. I'll share with you my story, my numbers, and my feelings on it, and hopefully it will be helpful. Maybe it will even make me realize things I haven't realized before.
A typical novel is about 80K-100K words long. This is literally the only piece of information I have gathered from writing groups, from other writers who told me about it, and such. This is a very broad number that includes adult novels in all genres, from literary to sci-fi to fantasy to westerns to even memoirs (for the purpose of this blog, though, I'm only covering fiction books). In this range, 80K-90K words is considered to be a more typical length, lower than 80K on the short side, and higher than 100K on the long side, with over 120K words considered too long. From what I heard about YA novels, the number hovers around 60K-80K words, and middle grade books even lower, 20K-50K words. This is not my domain, however, I'm only sharing with you what I heard and read about online. Now, from my personal experience of reading, I have read books that are total exceptions to this rule, for example, Chuck Palahniuk's debut novel (and one of my favorite books) Fight Club is only 50K words, and Haruki Murakami's 1Q84, another one of my favorite books, is 3 books in 1, and about 230K words long (I haven't been able to find the exact word count, calculated it from 925 pages multiplied by typical 250 words per page). Then there is Neil Gaiman's new novel, The Ocean at the End of the Lane, a rather slim book at only 192 pages, which would make it about 48K words (haven't read it yet, but thinking maybe Neil got to the point of being able to say more with less?). To look at my own stuff, the total word count for Siren Suicides is 245K words, with book 1 at 78K words, book 2 at 75K, and book 3 at 92K. I can keep going here with other examples, from Harry Potter to A Game of Thrones to everything else under the sun. This leads me to the next point.
You novel should be as long as it takes to tell your story. After having written only 3 books (well, 1 that split into 3), and writing my 4th one, I firmly believe in this. Throw all rules out of the window. Precisely because you are self-publishing, you can do whatever you want. Your story will tell you when it's complete. If it's only 10K words, well, it was never meant to be a novel. So finish it, publish it as a novelette, and move on. You might still make it into a novel. For example, Hugh Howey, the awesome rising self-publishing star, self-published the first installment to his Wool story as a novelette at only 12K words. He then wrote 4 more novelettes, in the same world, added them and published all 5 together as one book, Wool, at 528 pages, so about 130K words. It really comes down to the story. If I may be so bold, I would suggest you to stop thinking about word count altogether and start thinking ONLY about your story. A great short story is better than a long drawn out novel that nobody wants to read. On my own example, I'm learning the lesson of saying more with less. I think I have overwritten Siren Suicides by doing 5 drafts. People who beta read 4th draft told me that although it was confusing, it was raw and charged, and after I have attempted to make it sleek and clean, I ended up expanding it to the point of being too long. I'm thinking about maybe coming back to it later and editing it down to one book, and republishing. We shall see how it does. But I can tell you that while writing it I didn't really worry much about word count. I wrote it for therapy, and it ended up being as long as it ended up being.
Listen to your readers, they will tell you how long they want it. This is something that is maybe applicable only to those people who employ a similar process of writing as me. I'm basically sharing my entire writing process and crowd source feedback, by making all of my drafts available for download on my site and sending them to everyone who wants to read them and give me feedback. In general, if the majority of people tell me something is too long, than it is too long. If they tell me it's too short, than it is too short. I believe in this sense, the more you write, the better you get to feel your own length of your novels. There is a certain rhythm, a certain tempo to your words, and it's what makes you YOU. If you try to be someone else, your readers will sense the lie and ditch you pretty quickly. So don't be afraid if you are a bit on the longer side. So what? It's you, stay you, please. Same goes for short. I would say, write as many flash fiction pieces or short stories as you need to write, to finally write a novel. Your story will tell you when it wants to be longer and become one. Strangely enough, I have never written any short stories, launching into novel writing right away, and I tend to be on the long side. Maybe it's me, maybe I need to write a lot. Only future will tell.
There. I hope this was helpful. I think the biggest takeaway from this is just to keep writing. Our stories will decide themselves how long they want to be.