One tip: Every Substack has a feed, which is a nice alternative to having everything dropped in your email in-box. You just append "/feed" to the end of a newsletter URL, e.g. https://simonw.substack.com/feed.
I've been doing adjacent work for my search engine[1], and found substack to annoyingly be one of the sites that employ bot mitigation for its RSS endpoints. If you fetch at a very low rate it works fine, but for these types of bulk retrieval.
Substack is also a bit of a pain to integrate with because they have zero useful contact information and direct all inquiries to a chatbot that is beyond useless, makes it so you have to guess how they want you to interact with their servers since there is nobody to answer questions.
