For 4 TB per month you dont need anything special. Im running a RX460 which gives me 12000 nonces per minute. Meanwhile i run a i5 4600k processor giving me 8000 nonces/m on top of that.
As for ram. Ram is used alot in both the plotting and optimization process. Ive found that setting more ram doesnt neccessarly up the speed. In some cases putting it to 512mb have been faster than 1024. The issue is with many processes running you can run out of ram which will freeze your comp. Id suggest at least 16gb. Preferably 32 and you wont have to worry.