It’s great to hear that you are taking the community offline. I really believe communities thrive when we get face to face.
You strategy of starting small with informal get togethers makes sense, and is certainly where I would’ve advised you started.
The method I use is to “sow and reap”, i.e. “sow” the message that there is an offline meet up. Then you “reap” the ones who turn up or show interest. Reaping means that you gather them together, and invest a little more into them, because they showed interest.
You will find that people who you think will turn up offline don’t, and those who you didn’t think would turn up do - so always make sure that you “sow” the invitation by opening it up. It’s the ones who display interest that you can build more with.
As far as the event itself goes, there are dozens of ways you can make it engaging, however I recommend that regardless of how you run it, what is critical is that you play the role of facilitator. This means you talk to everyone there. You are the one who gets to know people, and then introduces them to each other. Then, when you do a short talk to welcome everyone and talk about the community’s wider goals, you mention some of the people by name.
All this facilitating has the purpose of “joining the dots” for people, so that it is easier for them to connect to one another, and to the purpose of the group in an offline way.