Regarding traffic, you can load up multiple campaign layers for the same date range, then turn on time compression and watch them move within the mission editor. Pause it, then do some rough counts, then multiply by the average group size (assuming you know what that is).
It's then possible to get a rough idea of the shipping volume.
The game engine is actually better at IJN/KM campaigns in many ways than USN ones since it assumes the sort of chatty sub behavior that resulted in the horrible losses suffered by the 2 Axis sub services.
I suppose you'll need loads of special transport missions later on, too.
tater