I'd suggest 1GB for the operating system, plus 1GB per account.
For ten boxing, I'd recommend 11GB or more, purely for Warcraft.

Ram is pretty cheap, 16GB would be plenty but 32GB or 64GB gets you extra if you want to mess around with ramdrives or whatever.




With DX9, a 2GB card is pretty close.
If you can get a card with more ram, that gets you some headroom.

If you want DX11, I'd recommend at least 3GB of video ram.

It will depend on your settings, too.
I don't think anyone is going to run 10 accounts on ultra.




The SSD is not essential, but you can pick one up fairly cheaply.
You don't need anything fancy, for a gaming folder; only if you were putting your OS on it.

It is optional, you don't need one.
It's just once you have enough ram, nothing else gets you as much of a return on investment.
It will make loading textures much quicker, which will greatly impact your play in main cities and to a lesser degree in places like Tol Barad/Wintergrasp.