I think a major contributing factor to the size of the DPRK's armed forces is the lack of other employment (or busy work) for the population. When the population is conscripted and forced to support the military machine, threats to state stability are minimized -- even if at the expense of internal development or foreign relations. It's a common strategy in many underdeveloped countries (except where the military itself is unreliable, i.e. Pakistan and Saudi Arabia). So I do not think we can accurately conclude that the DPRK wants to "play with the big dogs" on the basis of the size of their armed forces.