Q: How many network adapters can be combined in a single Windows Server 2012 native NIC team in a virtual machine?

A: Although a native NIC team on a Windows Server 2012 physical host supports 32 network adapters, only two network adapters in a team are supported within a virtual machine (VM).

This isn't a hard limit but rather a supportability limit. This is documented in "Windows Server 2012 NIC Teaming (LBFO) Deployment and Management" in section 3.8.2, at the Microsoft website.