You can find it here: www.jmlr.org/history.html

The JMLR story and operating model should be widely known in academia as a clear success story for full open access. I have friends in the humanities and pure sciences that have no clue this is even possible

My opinion is that if you wanted to start a publication today, build on existing tooling, for example as an overlay journal, or using version control community hubs.
https://oad.simmons.edu/oadwiki/Overlay_Journals

This nicely written story with a great reveal in the middle is a good summary of the discussion about costs of publishing. There is no reason for articles to be expensive, other than profit to the publisher.

https://archive.blogs.harvard.edu/pamphlet/2012/03/06/an-efficient-journal/