I have made a significant if not enormous amount of money serializing novels on Medium. I’ve certainly made more than I would have made from an unknown author’s advance from a publishing house. Although that isn’t saying much. LOL.
I think your ideas are good ones, particularly the newsletter idea. I actually address the problem of letting my readers know when a new chapter is out with tag lists.
With each new chapter that I release, I write a comment with author’s notes in which I talk about the writing process, or what inspired me, or give some additional details not included in the chapter.
In that comment, I tag people who have clapped for previous chapters in the book, with the caveat of letting them know that if they’re not interested I will remove them from list right away.
It’s worked for me. I have developed very loyal readerships for novels that have gone into dozens of chapters.