Advice on purchasing network drive

I am running a Mac with multiple external WD drives. Looking at purchasing a WD network drive to save space, ports and offsite accessability. What is the difference between the EX4, EX4100, and DX4100. I currently plan in running JBOD mode. One as computer backup, one as an archive, one as a working drive, and one to swap archives in and out. Eventually adding a mycloud for offsite backup. Plan on using green drives as well. Any advice would be helpful. Thank you.

All this info is at wdc.com main website. (Imagine that!) Here:
http://www.wdc.com/en/products/nas/business/