Hi @cesarFuhr,
Determining the errors for a categorization or group is not built-in, instead you need to implement a custom renderer or binding for this. See this question for more information on how to achieve this.
Note that in general we don’t recommend implementing a form wizard within JSON Forms. This kind of UX is usually easier and cleaner to achieve by implementing the Stepper logic outside of JSON Forms and then use JSON Forms for each step.
Instead of a very large JSON Schema and UI Schema you could then maintain multiple independent JSON Schemas and UI Schemas and directly reuse the already existing data/error notifications of JSON Forms.