Oh, forgot to add: 4gb RAM, but maybe will bring that up to 6gb. That's low-ish on my list of priorities.
My current file serving and downloading is taken care of with old laptops running Windows 7 Ultimate and external hard drives, hardwired to my Asus N66R Router.
If I wanted to use FreeNAS, I would just install it on those laptops and call it a day. Those computers run multiple torrent clients 24/7, serve 6tb worth of externals via Win7 networking (mostly homegroup), and I manage all this off my desk laptop (with a 1080p screen) via remote desktop. Those servers have to render themselves, along with web browsers running on them, in 1080p. Core 2 Duo and 3gb ram isn't cutting it any more.
I'm planning to image my primary server laptop (again, Win 7 Ultimate) to the server os SSD and see how that works out. Actually saves me time, and there's no potential for loss. If that doesn't work out I've got a copy of Windows Server 2012 ready to go. I'm just happy with the way all pcs are win 7 (and main desk laptop is win8) - they're on the same level. I don't need a server to manage them, just to talk to them. That being said, Win Server will do what I need it to do, I just don't need most of those features and frankly they have annoyed me with the limited time I've spent exploring it.
Oh, and this server is going to also be the host for windows backup (both from my main desk-laptop which has a 240gb SSD + 750gb HDD and my ultrabook with a 128gb SSD.
I don't need features like dual NIC. At least, I don't think.