The hardware resource requirements for SmarterMail 16.x are not much different than with 15.x. Because the web conferencing functionality is currently integrated with a third-party provider, that resource is offloaded from your SmarterMail server. That said, with the excessive number of variables that impact bandwidth, recommending a bandwidth value that works across the board is tough.
For a 'micro-business' or small deployment, we would recommend running on a Windows Server 2008 R2 64-bit or higher, using .NET 4.5, IIS, a single-core processor, 2gb of memory and 7200 RPM SATA drive.
I hope this helps!