The biggest limiting factor to the number of bots/wows you will be able to run is exactly this "I will be using it while the bots are running" ... it is YOU
It is always better to have a dedicated machine running your bots. Just about every bloody piece of software running on Windows 7/8 uses some form of graphics acceleration nowadays which wreaks havoc with any games running, leading to more crashes and other obscure performance issues.
I have a dedicated botting rig with a quad-core Core i7 975 @ 3.33Ghz, 12GB RAM, 2 x 256GB SSD in RAID-0 and a single NVidia 580 which can happily run 10-12 windowed instances of WoW doing all sorts of stuff. It is rock-solid and never crashes because I'm sat on another machine, I just use a $30 Belkin Keyboard/Video/Mouse switcher when I want to take control of the botting rig.
- If you are serious, use Wired networking (you'll thank me later), wireless technology - regardless of the B/G/N generation - is always prone to odd issues and interference and the latency is always higher than a good old GigE cable.
- Don't bother over-clocking, components are rated at given Volts/Ghz etc. for a reason, the error rates on consumer GPU's rockets when you start messing with its clocks and it just makes your whole setup less stable and more likely to crash.
If you're prepared to spend ?3,200 on one ridiculously overspeced machine ... it makes more sense to build a decent dedicated botting rig, and a nicely spec'd PC you'll actually use. Whether you then buy one monitor and a KVM switch, or two is up to you. Bots aren't that fussed about graphics quality or your screen resolution -- you could run them in 640x480 CRT screens and they'd be non the wiser.