Historically, I've manually copied personal files onto multiple hard drives periodically to keep them backed up, but I just emptied my wallet getting certain files that were only stored in one place (because they were so large I didn't have space to duplicate them) recovered from a hard drive that failed. I'm hoping to prevent this from ever happening again.
My goal is not to run my whole operating system on a RAID - I just want a certain set of personal files on a 2TB drive to be synchronized with a second external drive. Furthermore, to take advantage of the expense of two drives storing files redundantly, I'd appreciate it if there was a way to set this up such that my system could leverage faster read/write times by sharing the load between both disks, and keeping them mirrored while i/o is idle.
Building on this system, I want to be able to have offline availability of a subset of these files (Documents, Pictures and Music, but not videos) on any of 3 home computers. If a file is changed locally on any machine, which later reconnects to the network, I'd like changes to these files to be synchronized back to the main 'server'.
I'll do my best to illustrate my goal. Pardon the MSPaint art.

I'm using windows machines primarily, so for the offline file synchronization, I wouldn't be surprised if there's a built in windows service. As for maintaining a RAID 1 using an external, though, I'm completely in the dark. I'm somewhat familiar with operating systems running on top of a RAID, but really what I want is a 2TB external drive that is mirrored with a drive built into the PC, but can still be disconnected so that I can travel with my files, and re-connect it at a later date to restore the RAID.
Perhaps a RAID format isn't the ideal solution here. Maybe just some software that constantly synchronizes files between multiple directories. A huge plus would be if I could do this while the 2TB external is formatted as a FAT32, so that I could still connect it to Gaming systems, etc.
EDIT I think "Offline Files" will satisfy my need for remote file access from machines other than my "server", but in terms of the RAID 1 setup, is there any way I can experience read performance improvements at the same time? Seems a shame to waste 2TB and get nothing other than fault tolerance out of it.