In my opinion, I would do a combination of both.
If I was doing something like this I would make my cards an actor. That actor would have a “Widget Component” on it. That widget component would refer to the Widget asset that represents the card face.
That way I can use widgets to layout the card faces while keeping the nice feeling of the cards being actors in the scene.
In your second picture, change your “Plane” component to a “Widget Component” and then point that widget component at the card widget you created in the first picture.
You’ll probably have to adjust some settings and scale on the widget component to size it properly and look right, but that’s just tweaking some component properties.
Good luck!