I find 1GB works great with easyengine for a single wordpress site. I had a 2GB vps and it was just going to waste. I actually can’t imagine how you could use more ram than that. Remember checking ram can be confusing on linux. For example this is my ram use
total used free shared buffers cached
Mem: 991 943 47 80 59 622
-/+ buffers/cache: 261 729
Swap: 511 30 481
It looks like I’m using all my ram, but the important number is the 729 on the buffers/cache line. That is my actual ram available as processes need it, otherwise it’s used for caching. At least as far as I understand, so I should be fine even with 512gb.