Now the On-Prem system requirements are available : https://www.microsoft.com/en-us/download/details.aspx?id=55496
To get it running the minimum recommended requirements are:
Total Number of instances(VM/Machines) : 21
Total number of CPU cores : 104
Total Memory : 408 Gb
This minimum configuration will estimated be able to support 240-1200 users.
To sum it up: Go Cloud . Much smarter.