You need links for two reasons, so people find your articles and so Google finds them and gives them more credibility because they have links to them.
Links for People – these are the links you put in emails and forums. Concentrate on linking to a few of your websites. Get people on your website – Have interesting content – People then follow links to your articles from your website
Info Barrel allows you unlimited links between articles on the site, use them. The longer people are on your articles, the more likely they are to find a relevant ad and to click on it
Links for Google Spiders – These are the links you use from sites like YouSayToo and InfoPirate. There is debate about nofollow and dofollow links. essentially the general opinion is that dofollow links are better because they might improve your article’s page rank in Google. Spiders follow all links, so even a nofollow link will help Google to find and scan your article.
You need to link to every article you write.
EDIT: My thinking has changed on links and I no longer build any links.