Thanks for the explanation, very helpful!
Adding to this, I wanted my custom stats to define the main stats, e.g. make the actor's HP depend on their Constitution etc.
I assumed I could do this via VisuMZ's Core Engine and used this command:
<JS MaxHP Flat: ( $sl.getStatLevel(1,"brw") * 2 );>
However, this causes a ton of error messages in the dev console at startup about "maximum call stack size exceeded" (see the image). This happens even in an otherwise completely clean project. Do you have an idea what's going on and how I could deal with it? Or is there a better way to achieve this result? Thanks a lot!