650 WhatsApp subscribers. What should I do next?

I have been running a WhatsApp newsletter (JustAnotherPM daily ) - which is essentially a broadcast message. Twice a week, I send out a short form article on an important product management topic.

I chose WhatsApp because:

1. Its easier and quicker for users to read messages on WhatsApp than emails.
2. I started with short-form content (1-2min read), which is perfect for reading on the phone.

JustAnotherPM has ~650 subscribers so far via multiple channels - Reddit, Twitter, LinkedIn, students from my alma matter, FB groups, word of mouth. Most of the subscribers are aspiring or new product managers. This is the niche that JustAnotherPM is targeting (at least for now).

The response has been great - readers are finding the content useful; they are asking questions and requesting additional content on specific topics.

I, also, have set up a community (on Mighty Networks) to help surface, discuss and answer questions that the readers share with me. The community has 50 members. This number is growing slowly and organically. Engagement in the community has been low.

I am at a stage where I want to grow this into something significant and meaningful. At the same time, I have many questions for which I don't have the best answers. I would love to hear thoughts and suggestions from IHers:

1. What should be the primary focus - keep growing the audience (subscribers), drive more users to the community, drive more engagement in the community, or something else?
2. I have been thinking of starting an email newsletter (for the same audience). That will allow me to share long-form articles, which I believe will add more value than the short articles. Is that a direction worth taking at this stage?
3. Is there anything else I should concentrate on that I missed mentioning above?

PS: I am already working on creating a landing page for JustAnotherPM