A problem we haven't solved yet is launching new communities with a plan that gives them a reasonable chance of success. Most people discussing a new community here will be the answerers, not the askers. Since we can't expect many of the askers to be here, there should be a plan to attract them. Right now I see only crickets chirping in Physics, with no plan to fix that other than wishful thinking.

@OlinLathrop what did you do for EE, which was also founded by experts who (I think) were more prepared to answer than ask? What can we learn from EE?

I did some deliberate outreach. I personally contacted a number of people I knew, told them about the new site, and asked them to spread the word. I put a prominent link to the new site on my SE profile. (I'm a bit dismayed that some of the other founders didn't do the same, and kept answering questions on SE. I was hoping they would all go silent, people would look at their profiles, and come here. Oh well.). I also copied and enhanced a few popular questions from SE to seed things.

Despite all the above, the EE site is growing more slowly than I had hoped. Achieving critical mass is hard. This is why there should be a plan for it before a site is launched.

Judaism seems to have gotten started well. Are you getting new people from elsewhere regularly, or is it that there is enough interest already among the Codidact folks? It helps that it's more of a community discussion among peers (at least that's my impression) than strict Q&A. It's not a bunch of followers asking a few rabbis for advice, for example. The peer-discussion style site is easier to get going because many users will be both askers and answerers.