By the time that HD 7970 can't game well on a single monitor, it definitely won't be a good idea to Crossfire it. Even if it was, the i5-2500k at stock settings starts to show signs of bottlenecking in certain games with the HD 7970 so that's another reason that 2 of them would seem like a waste with an i5-2400, especially on a single monitor.
And just noticed I forgot a dvd drive. Will get a cheap one.
That Kingston RAM you have linked up there is no good for these 1155 boards. They require low voltage RAM as in 1.5v RAM, and that Kingston you have up there is the old school 1.65v. Chances are it will mess up your controller.