Okay, I'll answer my own question... rank is known from the Rivals screen (accessible by hitting the targeting cross-hairs), and then clicking on Rankings tab, which is to the right of the title of the rival tab. A list of the ranks and battle points needed for each rank is presented along with the rewards for making rank. You want to avoid gaining in rank too fast, as it exposes you to more powerful rivals then yourself... take your time and "farm" (i.e grow your cash building and build up your army).
