Yes you’ve understood correctly, however with GRID 5 (which is available from Sept 1st), the vWS license has been replaced by vDWS.
Yes, the M60 will be powerful enough for Bentley MS, however you should now be looking at the NVIDIA P40. The P40 has 24GB of FrameBuffer, however it only has a single GPU. That said, it runs on the newer, more efficient Pascal architecture. Looking ahead, the P40 will have more features available to it because of the software developments of GRID.
3 & 4) GRID is licensed by "Concurrent User". So you only need as many licenses as you have users concurrently accessing the GPU resource. So for 2x vDWS users, you need 2x vDWS licenses / 20x vDWS users you need 20x vDWS licenses.
With applications like Bentley MS, you should be using XenDesktop, not XenApp. With XenApp, you will run in to performance / contention issues. I’ve used Bentley, so I’m well aware of how it uses resources. It can be extremely resource hungry.
I can only advise on my own experiences but depending on the size of your Bentley models, you may very well need the full 8GB per user, this also depends on how many monitors you use and the resolution of them.
Test the solution for performance and load before committing to a deployment strategy, as the results will determine which path you take and the specification of your VMs which will then define how many users you can fit per physical server. The M60 is a dual GPU card and it has 2x 8GB GPUs available. As you have 2x M60s in a single server, you have 4x GPUs to use. If you can get away with a 4GB vGPU profile, then you’ll be able to get 8x users on a physical server as long as you don’t hit CPU or RAM limitations. If you run in to resource limitations, then you’ll obviously have to reduce the user count until the performance returns to a suitable level. However you’ll obviously need more physical servers to support your 20 users when you scale out.
If you choose the P40, you’ll have more options in terms of capacity, as there are differing types of vGPU profile available. I’ve attached a .jpg of all available vGPU profiles for GRID 5 in this post: https://gridforums.nvidia.com/default/topic/1286/general-discussion/nvidia-announce-grid-5-update-/
So if you were to purchase 1x P40, and you were able to use the 4Q vDWS profile, then you may be happy with 6 users per physical server (remember, these are high performance workstation users, not standard users, so the density must decrease). Or, if you wanted to use the 8Q vDWS profile, then purchase 2x P40 and you’ll get 6 users per server (CPU and RAM permitting)
As said, the only way you’ll really know which specifications are best for your workload, is to test and see how everything performs. However, I would still recommend that you use XenDesktop, not XenApp. And As I’m sure you’ll know, Bentley is very CPU heavy, so make sure you have the latest CPU generation with high clock speed and core count, as Bentley uses both!