ADuM5028 and ADuM240D0 4 layer board layout?


I am using the ADuM5028 to power two ADuM240D0 isolators, and I am using a 4 layer board. So far I have followed the advice from from the two layer EVAL-ADuM5028EBZ evaluation board, adding the two ferrites. I was wondering what to do with the inner layers? Is creating a stitching capacitor like that suggested in AN-0971 and AN-1109 still necessary? 

I also wondered about the ground pours on the top and bottom layers, and whether they should extend into the gap as shown in the figure above, or be level with the pads as in the EVAL-ADuM5028EBZ:

Thanks for any advice you can offer!

added figure from eval board
[edited by: jimbles at 4:29 PM (GMT 0) on 30 Jan 2019]