I think it depends on how big your scenes are, as far as running maya goes, and it depends on what kind of previews you would like to make when you are compositing. When you composite with AfterEffects, it helps out to watch previews, but It caches everything in your ram, so you would need more ram. When I run Maya, My average scene uses about 700mb-1.1 gb of ram, but then again I make pretty large/complex scenes. It is a hard call just depends on what exactly you want to do. THanks,
Brian