How do I grow an engaged, curated newsletter?

https://keto.fm

How do I grow our keto tribe and maintain a high level of engagement? We started ~2 weeks ago and got 200 subscribers by posting in relevant subreddits. We got ~200 subscribers through a facebook ad. I'm not a big fan of ads, but wanted to test it out. It's worked well so far, but I'm concerned those signups may not be as engaged as the organic signups.

How would you grow a curated newsletter?