Very kind of Mattias to share his process in such detail. I'm doing similar experiments at the moment with a wristwatch-focused newsletter, which is still tiny but requires minimal effort from me - usually just running a command once a week. My flow is:

1. A python script checks the RSS feeds of a handful of relevant blogs and pulls in any new posts.

2. The script checks a couple of relevant subreddits and pulls in the top discussions.

3. The script combines the posts/discussions and sends them to a handlebars template.

4. The result is then sent to the SendGrid API to send out to subscribers (although I send a test version to myself first, just in case).

There's no commentary in the newsletter which would be nice to have, but my priority is on establishing a quick and simple process that works – fancy stuff can be added later if I feel like it. SendGrid allows me to disable link-click tracking within the newsletter, and also handles subscribing/unsubscribing through an embedded iframe[0] so that's another thing I don't have to worry about.

[0] https://mizeni.com/newsletter