1) you can apply a visibility ador to either a layer, or to a page. To apply a visibility to a page, use the pages panel in indesign. Double-click the required page to go to that page, then on the pages panel menu, select "dynamic spread visibility" and then select your visibility ador.
2) to create the logic, just create a visibility ador with simple boolean result - either true or false as to whether to show the page or not.
3) swapping layers/pages is not very efficient and is very difficult to maintain/update the document. If you have just two variations, this is ok, but if you have many variations you should re-think your template design to use variable images and text (or text file) adors to change objects on the same page.