Definitely felt a little off, but if I didn't know that this was a deepfake, I would probably accept it as real. As usual, I don't know if that fits more in to the "remarkable" or "disturbing" category.
Eh, I'm not entirely sure I would have. The effect is near identical to when you have one person behind another, pretending to be the front person's arms and hands - the motions just don't match up right.
Maybe people who use faces more than full body language are more affected by this particular one?
I kind of agree, but it's hard to separate knowing that it's fake from my reaction to it. If this were presented without that context, I might feel like it's off, but not necessarily question it, especially if it came from a source I believed to be legitimate.
I also think, on top of all your points (which I agree with), keeping it shorter would make it more convincing. I think with the current usage of social media, short clips created through some synthetic means will be harder and harder to identify.
