Regarding downloading videos -
This is one of the questions that I asked YouTube directly, which was: "If someone downloads a video, what's stopping them from re-uploading that video on their channel?"
Their reply was simply (paraphrased) :
You can only download videos on mobile, and when you do download a video it's cached in the YouTube app and not actually "saved" in the phone (like a video they shot).
So basically, if someone downloads your video, there is no chance that they will be able to just re-upload/steal your content. It's exactly like downloading music on Spotify so that it's "available offline." You can only access it through the app directly.
Hopefully this clears up some stuff about that
If you have any more questions, please feel free to ask!