The side, top, and bottom will all have exposed areas that need to be covered with a finished end panel, finished top, or under-cabinet skin.
A finished end panel can be used for all of these areas if you want. It is essentially the same product as a finished top or finished under-cabinet skin.
The sides of that exposed cabinet will have construction holes showing, just like the wall cabinet placed on top. So yes, you will need a couple of finished end panels for the left and right sides, and a couple of finished ends for the top and bottom.
Finished ends are usually ordered 5/8″ proud of the cabinet cases. This allows the edges of the cabinet doors to be covered slightly, creating a clean stepped-back, flush appearance.