12GB ram is pretty good but, I would recommend 16 to 32 GB ram. With all the new patches and reverbs etc coming out plus you're asking about running "universal patches" of every instrument for an entire orchestra. That's a hell of a lot of patches. I personally think 12GB of ram is a bit low to do all of that. If you were only running a few patches (2-3) per instrument is one thing, but you want to run universal mode for ALL instruments. You could start with the 12GB, but you might hit a wall (but you could upgrade to more later if needed and you don't mind throwing away a little cash).
That to me screams, 16-32GB of RAM and nothing less then SATA drives internally/externally. Also, if you can (which you should) get 3-4 hard drives. Put the operating system on HD1, put Brass on HD2, Strings on HD3 and Percussion/Elements etc on HD4. This is equally important in terms of performance for you (and all of us). If you try to sample all those universal patches from one drive at once, you might have serious problems.
Maestro2be