Not necessary, but not bad to have them. Embedding videos from YouTube will keep visitors at your site longer, if nothings else.

yes but you should have your own rather than send them away to a an external site from whence they not return

I think they add to your overall authority as a seller, and more and more people are looking at them, not wanting to spend the time to actually read a full blown article...So a requirement, no, but adviseable, yeah... : )

"necessary", no. BUT, they will help bring natural organic search traffic. YouTube is the second largest search engine available now. And, one way to rank your website higher than another is the help of videos "embedded" from YouTube.

Also, videos help keep eyeballs on your pages. This results in a lower "bounce rate" which is a ranking factor used by Google Search. So, videos help in more than one way.

No - but in some niches they may provide a better user experience on your site.

ROCK ON!
E