Hello, I'm new here (joined MSE 2 months ago, before hearing about Codidact). Hence please let me know if you'd prefer new users not to write on this Meta thread.
One of the most attractive things about MSE, for me, is its gamification of teaching mathematics: one can write expositions of interesting problems and get (at least some) feedback. This is very useful not only for teaching but also for learning mathematics (via the Feynman method).
My impression is that you as a community are attempting to leverage this element of the attraction by retaining the reputation system and also encouraging people to contribute self-answers and articles. I think this is excellent. And, as a small community, perhaps you have even more ability than MSE to attract such users as myself because of (1) the possibility to answer things thoughtfully instead of racing to answer a question before other people do and (2) the fact that unserious users will more likely be attracted to MSE (where they can get their question answered quickly) than Codidact (where the emphasis is more on the community than on the Q&A aspect).
What I would most encourage is to continue this track by making interesting questions and answers more visible for people who might enjoy engaging constructively with them (and, conversely, I think, making "homework-help"-type questions less visible; suffice to say that an established community can probably sustain such questions much better than a fledgling community). I'm just thinking off the top of my head, but here's one possibility: right now answers can be marked as "worked for me" and questions can be upvoted. But upvotes don't always correlate well with how interesting a question is; so perhaps add special flags for "interesting" or "uninteresting"?
A second idea: perhaps it would be feasible to *add* basic mathematical questions for others to answer (imported from MSE or otherwise–but, importantly, *not* importing their answers)? For instance, for group theory, add questions like "How to illustrate Lagrange's theorem?", "How to characterize nilpotent groups?", "What are different ways to prove the Sylow theorems", "What is a Frobenius group"? If Codidact users were encouraged to do this, I imagine the community would get a steady flow of interesting questions like these and thus begin to attract the sorts of people who are interested in answering questions.