Hi garycase,
1) I've got a small 3 drive server built around this motherboard that is currently hosting backups for both my and several other businesses. With all drives spun down, it is currently pulling 28W (this is according to my UPS that is powering it, I can't take it offline to try a Kill-a-watt test at the moment).
2) I don't use WOL, so I can't comment, sorry. As the board is so low power already, I don't see any reason not to just run it 24/7.
3) None that I can remember, but to be honest, I first worked with this board over a year ago (maybe two), so I may have forgotten something. I do remember that the first board I got off eBay was defective, but Supermicro's warranty covered it and they sent me a replacement that has been running like a champ for quite a while.
Unfortunately I never tested this board with 3 TB or larger drives, but I would be surprised if it didn't work. Nearly all motherboards support 3 TB and larger drives as data drive, but only newer ones are able to boot from them. In unRAID, this is typically not an issue.
In short, I highly recommend this motherboard for unRAID.