As far as video cards are concerned you have to worry about the video card being the same if you are running SLI, it is recommended that for best performance when running SLI it be identical cards, you can probably run SLI with different cards its just not recommended you do that since it could potentialy screw stuff up.

One other thing you will need to take into consideration is the fact that you will need a beefier power supply for your machine the card will suck up some juice and since you are going to be running multiple monitors and at such high resolution you will again start to use up more power.

I would recommend you going with at least another 1G of RAM since you will be pushing your machine quite a lot with the setup you have and I am unsure how well your CPU will take all this at 2.4GHz being dual core, it could probably take it but you will be taxing it since there is a lot going on.

As far as the splitters it also depends on the cards themselves, at work I have an ATI in one of the lab machines and it is being split and running 2, 24" Samsung LCD's there great, though I dont really get to use them much, wish I had the set up for my house but they would not fit on my desk.