Sure my main rig is for gaming too but the great thing about VM's is that you can boot them up/pause them/shut them down whenever you want, I don't tend to be gaming at the same time as doing lab work and vice versa.
The main reason you want an SSD is that you will get really good IOPS for running your VM's on. I used to run VM's on my storage drives (2TB 5400RPM) and they were dog slow to boot and use.
I then upgraded my SSD and moved the VM's to my old one, and they just work much faster from there.
There is some element of thin provisioning as well depending upon what you are installing. You can assign a 40-50GB disk to a VM but it will only consume the utilised space on the disk, so you can over provision your VM's a little quite safely.
A VM would only consume 5GB if you run an older OS on it, later ones like Server 2008 R2 will consume more space without any extras installed. My Server 2012 Template VM is 18GB big
Having a bit more RAM would be a good idea, I had 12GB on my old PC and 16GB on my new one which are both fine. I also recommend a decent quad core processor as you want to give each VM at least one, maybe two vCPU's to use.
Really your requirements depend on how often you want to use these VM's and how many you want to run. My setup on my main PC is just fine for the times when I want to run some VM's for testing Exchange/AD, and I can safely run around 5-6 VM's like this (not really tried running more than that at once).