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Hey there, in my opinion, the answer is both: try to build as much diverse back link profile as you can. One link from the old article, one from the new article to keep the naturalness. However, I'd start with the old ones with some DA to boost your site and then continue with the new ones since you have already the link juice. Also try to think as Google - "Why would anyone suddenly add a new link to an old article? Does it seem natural?"

I agree with the suggestion to make the page be a helpful reference, with sales being almost a side aspect of the page. My current favorite website for examples is https://www.webstaurantstore.com/guide/541/types-of-table-tops-and-bases.html. This page gives a lot of helpful information when selecting a table top and base for a restaurant (which bases are easy to clean around, but might take up more space, and so on). They do have links to product pages at the end, but the selling is not the main focus (yet I imagine it's still fairly effective). That's something other sites can link to that has good information, and you can get links from good sites.

The answer here is: it depends. Are these links a little bit shaddy? Or they are just generic web directories. On occasion number #1 I would disallow them. On Occasion number #2 I would not. It is never bad to have more links as long as they do not negative-seo you

Just posting to back Nicholas up! Totally agree with him

Hi, Content is content irrespective of the type of site it is hosted on. As long as the article is good enough for Google to want to rank it, then I wouldn't worry about this. I would recommend you have a read of this post: https://moz.com/blog/case-study-ranking-high-volume-keyword It covers a whole host of great information from choosing the content through to best ways to promote it. -Andy