Core 2 Extreme QX6800 Build questions.

Hey guys/gals, I'm getting a used Core 2 system in a couple of days. I think I got a pretty good deal, but I would like to hear what you think.

Here are the specs:

Case: Antec P180B
Mobo: EVGA nForce 780i SLI
Processor: Core 2 Extreme QX6800
RAM: Crucial Ballistix DDR2 PC28500 2x1GB sticks.
GPX: EVGA 7300GT 512MB PCIe.
HD: WD 750gb (forgot which model)
DVD Drive

I already have a HD 4850 gpx card and 4gb of Hyperx DDR2 RAM, which I'm going to use instead. I'm also going to invest in a ssd.

My questions are:

1. Can I use the 2x1gb sticks with my 2x2gb sticks (different manufacturers). If so, how do I order then in the slots?
2. My HD 4850 will work in this mobo, but two HD 4850's will not work bc it's a Nvidia board?
3. Is the Core 2 Extrene QX6800 special in any way? I was told it's easier to overclock (which I might get into).
4. If this was your build what would you switch/change?

Thanks!