Question about CF and dual monitor setup

hi i have 2 monitor.. 1080p as my primary monitor and 1600 x 900 monitor as my secondary monitor... im planning to buy 2 sapphire hd 7970 vapor x 3gb edition and connect both of them via crossfire..

extra info:-
my primary monitor 1080p ( 3D @ 120hz) act as gaming monitor and my secondary monitor 1600 x 900 act as my multitasking monitor( @60hz)
my question are:-
1) should i plug the video cable( i dont know what's the name of the cable.. vga, dvi, hmdi, etc etc) for 1 monitor each?? for example primary gpu connect with primary monitor and my secondary gpu connect to my secondary monitor? cuz i heard somebody say this will not work and cause secondary monitor to turn black and must connect both of the monitor cable into the primary gpu.. is this true? and if i connect the both cable into the primary gpu(crossed fire with the 7970) will this decrease the performance of gaming? please mind that i want 1 monitor for gaming and 1 more for multitasking (youtube or facebook)...if the method i mentioned at ablove wont work, how should i make it dual monitor setup( gaming + multitasking monitor as i mentioned above) works?
2) And let say i dont want dual monitor setup and i only want 1 monitor setup, will 2 7970 will benefit me for gaming than 1 7970??

sorry for my bad english.. any help would be appreciated..

edit - my spec
i5 3570k @ 4.5ghz
16gb gskill ripjawX ram 1600mhz
msi z77a gd65
corsair tx 850w psu