What you describe (newsletters, comments, blog posts, payments, customization) sounds very similar to what ghost.org offers. You can self-host if you want or pay them to manage it for you.
I already have a blog, want to keep it online as it is, and I have no problem writing with my current editor software. What I am looking for is a way to publish NEW content FROM NOW ON:
1. FIRST as newsletter, with its own associated blog. Just because that seems the only medium left that people who do read a whole article still tolerate
2. THEN, 1/2 week a post has been published there, migrate it out of that platform and into my existing blog, leaving in the platform just a "This post migrated here, just click" notice. Because that's the only way to guarantee that that content lives as long as possible, always at the same URL.