Youtube - My top Unanswered Search Questions

I'm a pretty big expert in online marketing and search marketing. I have ten years of practical experience and frequently attend sessions held by leading national experts. I consult with some of them.  Yet, there are some big questions about Youtube that nobody seems able to guide me on.

Youtube. Youtube is a huge search engine but I can't seem to find any info, even by original research, on how it works. My specific questions are in two categories. How does Youtube decide what video to suggest? And how does Youtube affect  Google's main search engine rankings?

 How does Youtube decide what video to suggest? 
1.  Which videos does it show in response to a search query?  How much is it like Facebook and does it tilt towards recently trending? How much does it operate like the traditional Google search engine and have a ranking that it mostly maintains?
2.   How does it categorize the content in videos? Does it rely on the keywords that we type in? The descriptions that the author puts in the "about"?  Or does it search it's own transcript of the audio content (as redacted by its own speech recognition software)? Does it look at other videos in the same playlists or by the same author?
3.  How does Google decide which videos to suggest at the end of a video? Does it look at other videos that might be in the same playlist?
4. What role does the number of started views and the number of completed views and the ratio of completed to started views play in these questions?
5.  Do links to a video increase the authority of a video's in its Youtube ranking? How about the number of times it is embedded?

Youtube as Content - What influence on the Google main search engine results? 
6.  What about the impact of outgoing links from Youtube? In the description section for a video on Youtube, there is a chance to link to another video or another site. Does Google count these links in ranking sites?
7.   If Google does count these links in the ranking, how does it grant authority to these links? Does it have to do with the number of views of the video?  Since the older the video, the more views, would it make sense for Google to weigh these links by views per month?