Hi Jooji,
2000 concurrent users is easy to fit into 2 racks, you can probably squeeze it in one, but it'll be full. I'd suggest against blades (my preference) but if that's something you're comfortable with, all the power to you. I would suggest against a hyperconverged solution for VDI.
In Win10 VDI - you absolutely want GPU everywhere. Win10 runs boatloads better with a hardware graphics processor. But keep in mind - you need fast CPU's if you're going to use GPU. CPU becomes the bottleneck for VDI VM performance when you add GPU.
If you have any questions, please ask away.