It looks like you figured out how to size the images in the divs. You can set the div sizes (to same ratio) and then set the picture to 100% width to fill the space.
To make more gallery divs, simply go to the Navigator view (right side, navigator) select the div and copy/paste more div sections.
For the hover icon - you would need to move that inside the div you want it to be over - from there you would set the position of the element inside that div. Again, you could use the navigator panel to drag the icon into the div you want it to be in.