Don't confuse a mirror with a nightly remote sync (in this case an Rsync to a USB drive)
If your files don't change much and you have decent network connection at both your house and your office then you could run the Rsync over a VPN between both.
Like I said, there are pluses and minuses to each RAID implementation. You have to choose the one that you feel best suits your needs and comfort level. Me personally, I like RAID5 for the economy of storage, good performance and safety of the data. Nothing is perfect but a RAID5 array, RAID6 is better yet, with a hot spare is hard to beat. Most of the better controllers will do a rebuild to the hot spare/s in the background in the event of a failure. The Adaptec likely will as well if you are running a RAID5 array. It is up to you though which way you go.
I am in the process of bringing this on line at my home.
http://www.xyratex.com/products/storage-systems/storage-F5412E.aspx Enterprise class storage takes allot of the worry out of storing critical data for me. I have allot of DVDs to rip and I want to do it once! If you look hard and hit fast you can pick up this kind of hardware for a song.
Mike