It’s OK to write long posts here.
If you have written content elsewhere, say in a blog, it’s OK to link to the content, but it’s also OK to paste it in if you would like to share directly. People are more likely to read it directly than follow a link. And if you cut and paste HTML content from a browser, it will be converted into markdown syntax, preserving bold, italics, and more. Worth thinking about.
I thought it would be instructive to look at other forums. One of my favorite threads on the Hobby-Machinist forum is:
This was extremely long-form and many people have been deeply engaged in it over the past few years, even though it takes hours to absorb. Lots of us have found it very enlightening.