In what part of the problem? You have four boxes. Treat each box as a separate problem. And the first two boxes you don't need to actually design the guts of, just be sure that you fully understand the information and how that information is represented as it is communicated from them to the other boxes.
Until we have firmly established the connections between the boxes, it is premature to talk about what might be inside them.
Until we have firmly established the connections between the boxes, it is premature to talk about what might be inside them.