Adding unused RAM will not benefit performance in any way.
You need enough for your largest project.
For DAW purposes:
In a perfect scenario, you want more cores *and* high clock-speed.
If it's a choice, you never want to choose more cores at significantly lower clock-speed.
ie: Some folks assume that Xeon CPUs would be best for DAW purposes (because they're more expensive).If said Xeon has double the cores... at 2GHz slower clock-speed, you're going to take a performance hit.The new i7 8086k is a fantastic DAW performer; six cores (12 processing threads) running at 5GHz.
With the proper motherboard, you can lock all 6 cores at 5GHz.
With quality cooling, noise certainly isn't a problem.