This is actually really easy.

On our page for managing departments, we do this:

Department::renderEditComplex();

…and on our page for managing employees, we do this:

Employees::renderEditComplex();

This renders a DatarecordEditComplex which is a complete interface for managing data of the designed type.

The complexities of what can be edited, validation and etc., are all built-in to the Datarecord object.

That's it.