Sixteen gigs should do just fine.  I got a machine with 8 gigs, and now I wish I had more.  I do a lot of aerial shots, and with an infinite terrain I can't add even the simplest EcoSystem.  It just never gets past populating the dynamic EcoSystem.  It maxes out my physical RAM and my HDD runs constantly writing to the page file.  It may eventually work, but I've never had that kind of time to find out.

John