How long wil this build last b4 it needs to be upgraded?

Thats one hell of a box there mate. Not sure what you mean by 'last you' but the spec will keep your progs running for three or four years at least (depending on what your gonna use it for of course). RAID is a disk configuration for backup. Evrything you write to the disk is automatically mirrored to another disk so if your disk crashes you can, potentially, use the mirror disk.