It's interesting times time again
I had the Substack app on my phone and took it off because I didn't like waking up to misery, and the Notes section was abused by people commenting on popular posts they obviously hadn't read but they wanted you to read theirs, and nuts to that kind of selfish crap. Blocking people didn't seem to stop them posting at you and being annoying, either.
1/
Ghost seems to be the platform of choice, either self hosted or paying. Also if you self host you aren't giving 10% of your income to people you'd rather avoid.