Although I am not entirely familiar with VMware Workstation, I hazard a guess that if there are 50 workstations, there are 50 VMware guests, and each workstation is using one of them, and there's a really big resource-rich host system running somewhere.
You can do something similar, if you have a host PC with enough resources. Each remote user will need one separate guest OS as their work environment. (There are built-in ways for more than one remote user to see the same guest but they'll all be fighting for the one guest's mouse and keyboard.)
As far as how many guests you could run, it depends on your host PC's resources. Take the following as an indicator:
Virtualbox is an application running on your host PC's OS, so VB will be subject to the CPU counts and RAM limitations of the host OS.
You should not count hyperthreading when counting physical cores. A four-core Core-I7 with hyperthreading has four cores for Virtualbox purposes, even though the host OS may show eight. Your
I5 6200U has two hyperthreaded cores, so the physical core count for Virtualbox purposes is 2.
A guest should not be set to have the same or more cores than the host has, even if the Virtualbox Settings will allow you to do so. So on the two-core I5 mentioned, no guest should have more than one core. The host must always have a core to use for itself. It is possible to have multiple guests that each have less than the full amount of cores but total up more cores than the host has as long as the guests don't all go full-throttle at once. (eg: I have run two 2-core guests, and a one core guest = 5 cores for guests on a four-core I7, with no problem, because the guests weren't always heavily using the cores.) It's a risk, time will tell how many guests you can run at the same time.
Ram usage is simple math: the total amount given to guests + the host's non-Virtualbox requirements < total host ram. There are some tricks to move ram between guests while running the guests, but live hot-swap from host to guests is not possible, and you can't get more ram than the host has. Disk swap files don't count.
Expect disk bandwidth limitations and sluggish data access in the guests when booting or heavy-running more than two modern OS guests on one platter drive at the same time. The head just can't move around fast enough. SSDs eliminate this problem.
