When you buy RAM it should say if it is registered or not. It is a little harder to find, as it does not go in most systems, but it is available at most computer stores. Try www.ncix.com
At the top of the page, you can click on American prices if you happen to not be Canadian.
The RAID 0 should be reliable for a month. If the drives are defective, the defects usually turn up right away, or else they are good for quite a while. But I am not telling you not to back up tho. At least backup your really important stuff, because things do happen. Doubling the number of drives to go from RAID0 to RAID0+1 is a simple process, but it takes quite a while, because it has to create a mirror image of everything that is on the original 2 drives.