I would wait on buying a i7 right now. The current i7 chipset is due for an update this summer. Although, the i7 is very good for multiboxing. What changed from the i7 and the Yorkfield is the on die memory controller. The memory controller on die allows it to handle operations much faster because there is a shorter distance to travel. For memory I would go with 8 to start off with. Depending on what your graphics card is going to be driving, a gtx 260 should be fine for 2 24". I would suggest the XFX GTX260 Black Edition for a GTX. With your hard drives, I would suggest you get at least another 7200 drive, something like 160GB or even smaller. This would be where you store your OS. Then make sure you put your swap file on your SSD.
The only other bottleneck I could see happening is low quality memory, but if your throwing this much down, I don't think you would buy low quality memory.
I have a little experience with multiboxing but a lot with VMware machines, so thats where all my infos coming from.
-The Stig
"Some say he's made of a titanium absestos alloy....They would be right."