5. How to make a field editable while creating, but read only in existing objects?

You need to make the name and category read only once a Hero is created. However duing the first write the fields needs to be editable.

You can do this by overriding get_readonly_fields method, like this:

def get_readonly_fields(self, request, obj=None):
    if obj:
        return ["name", "category"]
        return []

obj is None during the object creation, but set to the object being edited during an edit.