You have all but walked yourself through the setup process. 🙂
Create the document, 11x17 pages in facing spreads, 6 columns, all as you want that majority of pages. You may or may not want primary text frames depending on how you will build and flow your content in one or more isues.
Now create a second set of parent pages with 5 columns, as you want them.
Apply that Parent page to pages 1 and 4.
Done. With primary text frames enabled, each page will have a linked, flowing text frame of X columns on it. Without, you will need to draw in your text frames for each article or story.
🙂
ETA: And feel free to ask more questions if any of those steps aren't clear. They are pretty basic ID setup steps, but if you're really new to the app you may not have used anything but preset pages.
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