I think any of them would be sufficient and you can set the CSS to apply the font to the <body>. You'd have a CSS class for each font and that would be set based on their settings or the default font.
Are you using webpacker with this app or esbuild (or similar)? For now, you could try to take the stimulus controller from the code repo and add it into your app. Alternatively, and perhaps my current preferred approach is to use Turbo and a turbo_frame_tag with the src attribute. No javascript needed with this approach.
If it's just for local development, I would use the same postgres instance for both databases. It looks like your trying to connect to the postgres on localhost (::1) but should probably be using the name of the service (postgres, or whatever you named it in the compose file).
It can be. I typically default to “Application” in these cases because it is namespaced under features already and follows the Rails convention of ApplicationController and ApplicationRecord.
