I usually go with branded and generic anchors, unless I want to rank the homepage itself where I also use partial match anchor texts. I never take links from the author bio box, which is similar to a blog comment.
Can't say for sure without knowing the actual site, but you should know that all bloggers nowadays are selling links so it doesn't mean it necessary is a PBN website. I try to avoid as much as I can sites that all of their posts are sponsored ones as it is a matter of time before it takes a dip.
No, I didn't say that at all. There are good services here as well, it just depends how you use them. A diversify link package is a diversify link package, nothing more. You shouldn't expect to boost your rankings for a keyword like "best gaming mouse" or "best SEO software".
As for domain relevancy, you should do your best and optimize your article where the link will be placed on. RSOs technique is the one that I use to get a link from a site that is not 100% relevant to my niche/website and it makes sure that it pumps my rankings.