In general, modules share all data via the MRML scene and communicate via node modified events. You can also call another module’s logic objects, which is useful when one module uses algorithms implemented in the other. See more details in this tutorial: https://github.com/PerkLab/PerkLabBootcamp/blob/master/Doc/day3_2_SlicerProgramming.pptx?raw=true
Yes, this is available in Segment Statistics module. See details here: New Segment Statistics: Oriented Bounding Box, Diameter and More