I want to scroll these images from top to bottom. When they start to exit the bottom I want to them to re-enter from the top – therefore creating the illusion of infinite scrolling
Depends on your construction of the elements but basically you’ll want to create a keyframe with it right back in its starting position after the final frame of it leaving. You can do this either with individual boxes or with the “group” of boxes.
If you intend to have it re-enter before the last one leaves you’ll have to either do it as individual boxes, or using a duplicate of the group.
Then save that part as a composition and either in AE or more likely in Premier you’ll loop it as many times as you want it to run (or all the way to the end of your video)