There is no point of CF 4870x2.
Even a single card can max out every single game.You would be wasting money.
Maybe an year later you may feel the need to CF but now you should not.
And ya.........Corsair 1000w would be enough for 2 4870x2's.
I ran 2 perfectly fine off of a 750w for a few weeks, a 850w-1000w would be advised but the power requirements of today's hardware aren't stretching any 1kw PSUs quite yet. The Corsiar, as you said, would be perfectly fine.