can't really answer you question, but you might want to ask it down the hardware forum or over at BI forums.
hmmmm...wasnt there a limit of how many units you could set up in the editor..., plus there is no guaranty that the code in OFP will allow 200+ with good FPS. I'd check over at the BI forums to see if anyone has tried.
dual video cards, some motherboards offer a 2nd slot for additional video card, dont remember if its only for pcie cards though.
ATI was going to come out with a 1 gig card.
again, I'd check in the hardware forum