A good combination of all of it. I'd say social signals doesn't work too much, I had greater success with backlinks only, and ofc views, comments, faves, likes etc... Make it look natural!
Yup, but don't market it as an ebook like that. An example could be: How to grow taller naturally.
You'll make a video promoting the SOLUTION to this problem. Like, "Download the complete guide from the link in my description." The video itself could be a person from fiverr talking about the subject, and preselling the viewer to download that report. It's as simple as that!