I don't believe Number of Cores is a value that's available.
The "Processor" datasource in the Computer (System Information) report category does return one row per socket, so machines with multiple sockets can be easily identified.
Otherwise, I think you may have to infer "number of cores" from other attributes, perhaps Family and/or Model
As for whatever you're getting from the Managed Computers node, that is exportable to Excel, as well as several other formats. Select the desired row(s) and click on Export. A dialog will offer a selection of radio buttons to choose the desired export format.
I will check it out in the morning and let you know how it works.