I don't know Substack, but I checked out a couple of blogs prompted by your question.

I read their "how to get paid on Substack" article and they work up some revenue projections/examples based on things like a conversion of email subscribers to paid monthly subscribers of 10%. That seems really really high.

I would have estimated an email campaign open rate of 10% not a conversion rate of 10%. I would have expected a conversion rate in the 1% range or less.

In my experience, people in general don't really want to or expect to pay for information on-line. They will pay to be "entertained" through for example Patreon, but not for information and particularly not text based information.

I hope you find success but I would be cautious about using some of Substack's estimates. Hopefully I am wrong.

For what it is worth, your NewsCatcher project looks interesting. Is your intent to use this new blog as a practical example of using it?