The question could be summarized as :
How do i create data marged document with a double page spread? I am currently able to create multiple pages from a single page layout.
Data Merge only allows the single page layout, but you can change the doucment to facing pages after the merge. If you need a wider margin in the center of your doucment, layout adjustment will allow you to acomplish this.
Set your initial document with the wider margin on the left. Once you have your merged document, go into layout menu and allow layout adjustment. Then, when you change your doucment to facing pages, the wide margin with become the inside margin, and the page contents will shift to match.
unless i misunderstood the post, i don't agree with the above poster as this is something i do often.
i use a trick to make merges with facing pages to make diaries. this trick will only work with merging two-page spreads which start on a left page and end on a right page.
the trick is:
1) make a new 1 page document and make sure "facing pages" is turned off.
2) with the new document open, go to the pages palette and add another page by dragging and dropping an A-master as page 2 of the document. at the moment the page will be one on top of the other.
3) still within the pages palette, right (or control) click the page and make sure that "allow document pages to shuffle" is turned OFF (that is, no tick next to it).
4) make the merge as you would like it to appear. when ready to merge, merge as per normal, and the new document will start with a left hand page like so: