I'd find a way to make it cheap for you (in time and energy) to iterate such that the one-off content that you're providing can be used as stepping stones to a paragraph, and then a chapter, and then a book.
As an example, I've written thousands (!) of customer support messages, via email, chat, or reddit, to help my PhotoStructure beta users.
I've found that the second or third time I answer a question, either I need to fix the product so the question doesn't show up again, or I transcribe my response onto a new page on photostructure.com. In my case, it's just `hugo new content/faq/post.md` and then I dump the new content into the new page.
It doesn't have to be an elaborate post. Perhaps a bit more nuance or detail than my customer support reply, but not much more than that. Sometimes it's only 1 paragraph.
I've found that these "humble starts" can then be iterated on fairly easily, as inspiration comes to you.
As an example, according to git, I've made 15 commits to <https://photostructure.com/faq/library/>. The first iteration was just a handful of sentences I wrote as a response to what I meant by "library."