RAM will only become a major factor if you find yourself running a large number of samplers that eat up resources. I've never noticed an improvement beyond avoiding crashing when loading projects too large from my RAM capacity. Even with the consideration of more samplers in the future, I would have to tell you that 8gb is enough (read: I have no idea what libraries you intend to use, or how you'll use them I often hit my ceiling of 12gb but most often because of the nature of the project!)
The OP mentions running orchestral instruments; I have LA Scoring Strings, CineBrass Core and Pro and quite a few percussion libraries as well as Hollywood Winds and the like. Just running a full LASS orchestration will EASILY max out 8 GB RAM, before you've even started on the other stuff!
Cheers,
Sam