Back ot the RAID topic: if I just have this two-drive system for a while and upgrade with another hard drive later, how easy is it to creat a RAID with an existing drive with all its data? How easy is it to isolate the other drive that won't be part of the RAID?

It all depends on the particular RAID controller. The expensive SCSI ones I work with never allow a drive to sit attached to them without being in an array. It has to be at least a single drive RAID 0. They do allow expanding the array by adding new drives. Also, they allow RAID migration, thus going from a single RAID 0 setup to a RAID 1. But again, it all depends on your particular controller. If you have an idea of one, I recommend you go ask in the forms at www.storagereview.com , they seem pretty helpful and do talk about different RAID controllers.