This is currently not possible in yEd but it would be nice to have, so I changed it into a feature request.
Since your data is imported from Excel, it might be possible to do this with some help from Excel and the yEd tool Properties Mapper. This tool can be used, amongst others, to scale the node height according to a custom property values (i.e. node or edge data). Unfortunately, it is neither possible to scale according to the number of edges nor to store the number of edges in a custom property. However, it should be possible to calculate the number of edges of each node in the Excel sheet and import it as custom property.
For more information, please see the manual page about Properties Mapper and the questions in this forum about this topic, and let me know if you need more help.