Yes those are ghost nodes, probably from failed pairings. Sometimes they cause major problems for some reason, other times they are harmless. How To: Remove Ghosts using hub tools or a UZB Stick
No does not matter, either way the device and node should both be removed. I prefer to just do it from the z-wave details page, I feel like I have more control. The "Remove" button from the device page is more like a wizard that walks you through it. The device page will however warn you if your device is still connected to apps.
Usually when I exclude something that is in SS already, I will see a SmartStart join message in the logs within 30 seconds of the exclude happening, then device pairs 30-60 seconds later. I have done it at least 30 times if not more, with the ZEN16/17 and also some motion sensors. All for driver testing.
