Nope. You should be good. (The way you "check the BIOS" is to mount an additional video card and see if it runs or not... )
Sometimes... up to a point. Usually only when a problem needs to be fixed... rarely to add functionality. As a general rule... if you're not having any problems, no need to update the BIOS. (Update is not without risk. Sometimes leads to hosing-up your BIOS... sometimes after messing it up, there is no fix except to replace the chip.... wouldn't think that is common, but there have been stories... A failed update is more likely to make your machine not run/properly and you have to wait until the maker figures out what's wrong and posts a fix.)
I suggest you take a look at Matrox Triple Head To Go http://www.matrox.com/graphics/en/products/gxm/th2go/ or buy/build another PC
The two cards do not need to be identical. Identical usually ensures they are compatible. Mixing different makes for the graphics chips (e.g. ATI versus NVidia) will likely have compatibility issues. But within the same make, mixing models in the same series or mixing models in different series may still work. For example, I have some EVGA 8600 GS and 9600 GT cards on the same machine and they work okay together.