I basically have no idea what I'm doing either (at least that's how I feel, even after my CS Bachelor). But I had a urgent need for redundancy (a NAS does not necessarily provide backup functions, but rather redundancy, that's a difference (at least if you rely on RAID)) with lots of bytes in movies and music, and now my growing photo library after getting my DSLR. So at first I wanted to get a HP Proliant Server and use that as a NAS, but it was limited in slots / bays and it just had too many disadvantages, which is why I decided to go for a QNAP TS-412 with (at first) 3x 3TB WD Red (the NAS drives). The configuration was as easy as you could imagine. I connected it, plugged in the 3 drives, started it up, decided what RAID I wanted (I went for RAID5, because that saves me from hassle when I add a 4th HDD and it uses very little space, and speed was not an issue, since it was mainly for storage) und it was basically set up. Of course, a little bit of user management and privileges through the interface, but that was pretty easy to handle, too. And as it's basically only me that uses the NAS, I could just admin the shit out of everything and give me just all privileges everywhere, which (I guess) saved me a bit of a hassle toying around with the authorizations. After that I created the folder, added it as a network drive to my PC and it was basically already functioning as I wanted it. On top of that I wanted my torrent client to run from the NAS, and even though it's only an ARM processor, it works just as fine. QNAP offers some pre-packaged setups, which are super easy to install, so I got transmission and got that set up and running super easy, too. Added a GUI for Windows and my Android and voilà: I had everything I wanted. I can control my downloads from everywhere in the world (which is handy when I'm on a business travel) and I feel secure with my data being secured from HDD failure (see, redundancy, not backup). On top of that I added the movie folder as a resource for my RaspPi with XBMC and I have my whole library easily accessible and fancy looking. Everything on the QNAP is easy to handle, and the latest firmware also added a huuuuuge overhaul of the interface, making it even easier. I may not use it the most efficient way, maybe not the most secure way, but it works just as fine as I wanted it.

The next quest will be upcoming this weekend (which is funny, because I just placed the order yesterday and now I see this topic), because I ordered a 4th WD RED 3TB to add to the last unused bay of the NAS. If everything goes well and as user-friendly as I hope, I just put it in the bay, the raid system is rebuilt and after a little bit I can use it with 9TB instead of 6TB. I don't know if that's how it will work out, but I remember that there's an easy option with a configuration wizard which simply has the function "Add another drive to the RAID array". And the community in the forums is pretty active, too. So I'm not too worried about that, even without being a super nerd, who handles connecting to the NAS via Putty as it is nothing.

All in all I'm more than happy with my choice, even if it was the slightly more expensive way (compared to the HP server). Easily being able to add another 3TB is golden, the management is easy, I love my media center with XBMC (a NAS + XBMC is just sooooo good) and having torrent running 24/7 and accessible from everywhere all the time is just super handy and nice (without having the desktop running). I even have that QNAP standing 2 meters from my bed and it's so silent that I don't mind that. So yea, I couldn't really help you with your specific problem set, but I hope I gave you a little insight how I handled things about a year ago, when I was in almost exactly the same situation.

Edit: Now that I think about it, we're not in exactly the same situation lol Well, kinda, but I had 2TB of stuff and I solely rely on redundancy without backups. But I have no suggestion how to handle 12TB of data right now, haha. Maybe decide for a solution that is almost full right now, but easily vertically scalable, so that you can add resources one after another, whenever you need it (like I did with my RAID5, at least I hope so). The problem I see there though is, that I feel like after 4-bay NAS, you hit the end what's considered "homeserver" and you get into business spheres, which is not price-friendly at all anymore. I have no proper solution, but I'll keep track of this topic and let us know what you will end up with :P