4 Monitor setup

Here is my question(s) and thanks in advance for taking time to read and reply

I am setting up 4 monitors and current graphics card is 460 gtx set up for dual display. I dont do gaming or anything. Now I am running out of room for watching stock charts, chat, browsing and I am tired of minimising windows etc to see things.

I dont want SLI just 4 monitors-here are my questions.

Will any Nvidia card work if I keep the 460 gtx as my primary card ?
Are Nvidia (or for that matter ATI too) drivers card specific or same for all cards ? really confused about this one.
I just need 4 monitors, If I add a cheap card like GT210 will it display another 2 monitors ?
How much of a performance hit will my display on primary card take - will it be slowed to lowest denominator or still retain some of it ?
Will the performance of Primary displays be same if I am not using the additional two displays ?

My current motherboard is Asus P8P67 with 2 pci-e 16 stlots that will run at 8x if two cards are added. Even at 8x it should be more than enough for my needs. CPU is 2500k i5 sandybridge, 12 gb ram ddr3.