Update which folks might find interesting.
Synology did respond to my email, and it was within 48 hours. Not super-great, but in 2012 and the state of technology vendors, it really is not that bad. Very nice, personable and and professional response and interaction. Very pleased. I would purchase Synology (so far) with this support-model in mind.
So after an email exchange I turned my NAS back on and found I could still "read" from the crashed volume. So my offload copy is in progress (slowly....)
Of interest, The "new" Disk-4 remains invisible, I got two "I/O error" on Disk-1 overnight, and also a notice that Disk-2 had crashed (and a few "I/O error" notices).
It now seems probable to me that this is mostly a DiskStation-based event/problem. I think Disk-4 (the original, not the replaced/invisible/non-initialized Disk-4 in the NAS now) was clearly defective which was the compelling cause. But I do not think Disk-1, the new Disk-4, and now Disk-2 are defective/failed. We'll get more information after the offload when I do some SMART tests.
Do folks think my NAS unit is defective? Are there settings to mitigate the issues?