Just like TheFirstKel said, licenses for this game are per platform, but not specific to a machine, so you can play on an unlimited number of Windows machines (or PS3/4s or whatever your platform of choice may be) without having to repurchase the game or any expansions.

EDIT: also, yes if you are going to be using different IP addresses (most likely) on those accounts then a security token (physical or app) will save you a lot of trouble resetting passwords (and free teleport to boot!).