I've been creating some content for a site that has 5 existing pages. Now I'm linking it all up. I've created 12 new pages. Is there a rule of thumb to how many internal links each should have too and from it? Do these new 12 pages need to be heavily linked from the old site. Their content is not particularly important to the function of the site. They have been created round several keywords to rank well in search engines.
It really depends on what would seem intuitive, there are no rules of thumb.
If you don't want to add those pages to the main navigatio of the site, then perhaps you could link them all together through a footer at the bottom of the page. Another option is to create a site map, link from the site map to those pages, link from the index to the site map, and link those pages to each other.
There are several alternatives, you just have to figure out what's best for your site and target audience.