If I posted this on a blog: "Yes I agree with this post. On New York Luxury Cars website, it mentions this as well. These cars really are the best" Would this get me good anchor juice for "New York Luxury Cars".... or do I need to use a signature??
"Do follow blog" means that the username link on comments will not be no-follow. Don't quote me, but I think that links in the body of comments are do follow for most blogging platforms by default.
Having relivant info on the page is important for linking, S.E.'s pick this up. You will definitely have more "link juice" the more relivant the page you are linking from. Signatures not necessary, you can check page script to see if "Follow" or "No Follow" is being used..
Yes, having a relevant backlink is much better. Non-relevant backlinks won't hurt, but they won't be as beneficial as relevant ones.