I bought a brand new WD Easystore portable 2 TB HD in October, 2017, and just now, 5 January,2018, opened the package and tried to use with my iMac 5k Retina 27 inch, Late 2014 desktop computer, also running OS 10.13.2.
I am getting the same fail message you are - “MediaKit reports not enough space on device for requested operation.” This should not be the case as my iMac drive is 1.1 TB and is only one third full. This came up with Time Machine, but then Time Machine doesn’t see the HD. Using Disk Utility the HD shows as disk3s1 (yours is disk2s1). Nothing works trying to erase the disk - not the proper Mac OS Extended (Journaled) format or any other formats erase, although it opens a box that says it is erasing.