All processors for computers now are multi-core, except for the low end and low power devices.
Don't know what "extra" RAM would be, any RAM you have in the system is not really extra. 4 gig is plenty, many systems now come with 6.
Same with the hard-drive "larger" than what? A 1 TB is pretty much a standard and is enough to hold a lot of files. You may want a couple of 2TB drives setup in RAID1 for redundancy so you don't lose any files to a drive crash, plus an external drive for additional backups.