You might want to avoid reimplementing deploying known - and complex - components like postgres, it's better to grab such things as a dependency from someone who's already done so.
It's also quite suboptimal to store secrets - like the postgres password and such - in a ConfigMap, and requiring the user to manually create objects in order to be able to deploy your chart is also a major hurdle towards actually using it.
I wrote my own Helm Chart for lemmy as well, not really finished with it either though as I want to make the deployment safer, and also better support gitops.