I've got a regular ATI Radeon that runs two and then bought an external(USB) monitor plug in. If you've got the money, it's worth getting one card that supports all your monitors though.
Get the new ATI's 5xxx series - the 5750 is fine driving 3 (!) screens at a higher resolution than yours and uses only 25% or so of the power of older models / nvidia doing so (which means less cooling needs = less noise). As was said, the resolution is not that high by technology standards
A height of 1080 or 1200 makes quite a difference. And keep in mind the amount of time you are going to spend in front of your screen: hundreds of hours, and probably thousands. My advise: do not care about the last $100 more or less for a screen.
No. That is what I have connected to one computer. Hopefully soon I will have the entire setup (8 x 24") back.