I would probably just draw out 2 frames on the master page, select them and choose Object > Fitting > Frame Fitting Options, then choose Fit Content to Frame from the Fitting popup menu. Now you can return to the document page, and place the PDF with the Show Options checkbox turned on, so you can choose all the pages you want from the PDF. That loads up the place cursor with the pages… Now you can just click, click, click all the pages (adding pages as necessary with a Command-Shift-P or Ctrl-Shift-P). Each time you click on a frame, it places another page and automatically scales it down to size.
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