Removing backlinks, especially ones with money anchor text, will most definitely cause your rankings to decrease. I can only assume you did this because you viewed the links as spammy or something that could eventually cause you future ranking problems at an algorithmic or manual level. If that is the case, you probably made the right decision if you are hoping this site will rank for the long-term.

Instead of restoring those links, try to find a way to create a few new ones that you feel are safe for the long-term.

Hi Joni-

This is indeed possible, although it is a bit of a struggle to accomplish. Look at my answer on this similar question to get started and then follow up here with additional issues if you are having problems.

http://moz.com/community/q/trying-to-link-a-legacy-youtube-account-to-a-google-page-the-option-isn-t-available

Hi Jenni1,

You are right to be concerned. Do not use the canonical tag like you have described above.

I would recommend putting that content on it's own unique page. Then, pull in the content to your product pages via a an ajax request to pull that content into the tabbed area. This would make the content visible for the user but not a part of the page html for the search engines.

I'm going to disagree a little bit with the other commenters. I've done quite a few large scale redirect projects and I'm not 100% opposed to using a "dirty sitemap" for a short duration. The better option is to leave some internal links pointed at the old URLs. I know what the search engines say, but I also know what I've experienced when it comes to getting 301'd links crawled again.

Read this post by Everett Sizemore for more info at what I'm describing:

http://moz.com/blog/uncrawled-301s-a-quick-fix-for-when-relaunches-go-too-well

No, you do not need to include links to youtube.com in your website's sitemap. Google has no problems indexing videos on YouTube and your sitemap is meant to help Google index content on your own website.

Video sitemaps are a must if you are using self-hosted videos (ie- not a YouTube video player). To learn the basics of video SEO, go here: http://moz.com/blog/building-a-video-seo-strategy