Google is your friend. You can easily learn many of the answers to your questions by doing a little bit of searching. Doing some research on your questions before you post them on a board shows that you are really interested in the answers and have some respect for time and talents of the people you are asking to respond to your queries.
Linux is a modern operating system. Linux handles multiple monitors without problems. Many present day high end video cards are capable of displaying on two monitors at the same time. I have such a configuration myself.
Most current personal computer configurations are limited to 4G of memory which Linux can handle comfortably. I do not know what the upper limit is on it's memory handling capability.
I suggest you search Google with the key words RAID and Linux to learn more about those topics.
You might also find that some research on the topics of sound cards and multiple channels will enlighten you on your questions in that regard.
Linux is currently used on devices such as PDAs, Wireless Routers, Personal Computers on up to Super Computer configurations. Search for Beowulf.
