What are your current PC specs? What games do/will you run? If you've got an older computer that would need upgrades anyway to run the games you want then that's one thing. If you just need a beefier GPU, you'd be better off getting that GPU and a server to do your study work on.
If you get a server, I would NOT recommend a 1U server. They are quite loud due to the small fans. A 2U or larger server would be better as they can use 80mm or larger fans. Sure they can still be loud when they spin up but it won't be anything like a 1U server.
I would normally recommend 2GB minimum for Windows 7 but in a VM and if they aren't used as a desktop, then 1GB would probably be good. Since it is mostly for testing and learning, 1GB is also generally sufficient for servers and even sometimes more than enough. 8 session at 1GB each, well you can do the math
and 16GB should be more than enough and have plenty of headroom.
I'm partial to Dell personally. My servers I mentioned above are 2950 III's and one 2950 II. The main difference is the II uses 1st gen Intel CPUs (5100/5300 series) and the III uses the second gen CPU (5200/5400 series). The downside is they use FB-DIMM memory which isn't as cheap as DDR3 but many systems on ebay have 16GB already anyway.
Both models can come in 2.5" or 3.5" form factor for drives and do accept commodity SATA disks. Given this is just for personal use and testing, SATA is probably just fine and will be cheaper than SAS drives. If you give each of the 8 VMs 40GB thick provisioned, you'd use up 320GB, so use that as a basis for storage needs.
Here's a 2950 III with 8x 73GB 2.5" SAS drives. »www.ebay.com/itm/Dell-Po ··· 6c7b306b
That would give you ~500GB in RAID 5 or ~300GB in RAID 10. Either option should give you enough storage space for your needs.
Here's a similar 2950 III with 2x 146GB 3.5" SAS drives. »www.ebay.com/itm/Dell-Po ··· cfca5955
Use these in RAID 1 for the host OS and add in as many SATA drives in the remaining 4 3.5" bays as you need/want for VM storage.
As for the seller I picked, I've bought things from them before and they've always been a pleasure to deal with. They're local to me so I haven't seen what their shipping skill is like unfortunately. Either of these choices is less than your listed computer upgrades so that to me makes it worth the investment as you aren't using your computer to do the work on. You'd need to install Server 2008/2012/Hyper-V Server to run Hyper-V and that may not play well with games anyway making your original idea possibly a no-go (especially with Hyper-V server).