I don't know how well Windows would be able to support an 18 monitor setup; you might not be able to use all the monitors at once. I don't know for sure though since I have never done an 18 monitor setup. My guess is that if it works well, it will look epic. Could I also ask, what will you do with 18 monitors?
to be honest i have seen 12 monitor set up working just fine on 1 computer. I am going to set up 9 monitors for gaming, 6 monitors for excel and accounting and 3 for web pages. My concern is that there wont be enough power but from what i am reading 3 cards should have atleast 1200 watts. but then what about cpu and motherboard and the rest?
Yes. Also, your CPU should be powerful enough to process what's going on between all your monitors. GPU will do all the work where gaming comes in, but your CPU will have to be able to process your web browsing and excel work over 9 monitors.
I will be purchasing an i7 3770, 2600 ( not the K version ) or i7 3820. The reason is because they have the Intel® Virtualization Technology for Directed I/O . which one would be better for my purpose?
Also is it possible to connect 2 PSUs to 1 computer. 1 psu powering motherboard, HDDs etc while the 2nd powers the 3 graphic cards? I will design and build my own case so i will take space into account.
I'm sorry, but I haven't had much experience building computers in the past so I can't answer your question about connecting 2 PSUs to 1 machine. To asnwer your question about the CPU, if you need Intel Virtualization technology for your work (and that's it) then get the newest and most powerful CPU - something within your budget, of course.