If you knew anything at all about North Korea -- which you all too obviously don't -- you'd know it was a new Reich dressed up in Communist Party clothes controlled by a viciously mad elite which terrorises its citizens into submission and consigns entire families to punishment camps (aka concentration camps) from which they're unlikely ever to return. Like Nazi Germany, and Hitler in particular, its contempt for its own ordinary people is exceeded only by its adoration of military might. It is not merely the lunatic in the global room but the homicidal lunatic in the room, one which believes it can do and say anything and, indeed, does precisely that.
Your question : 'What could a well funded capable nation achieve in terms of havoc if this is what we can expect of North Korea?' manages to betray your own epic ignorance whilst answering itself at the same time, because North Korea, lunatic state thought it may be, is 'well funded' and is 'capable' -- capable, unfortunately, of anything.
For now, the lunatic is waging cyber war. It needs to be neutralised before its madness takes it from the virtual to the real because the lesson of history is that if you want to protect your future, you don't sit on your arse doing nothing in the present. Capable, well-funded, and dangerously deranged though it is, North Korea is one against the many. The many should be hitting back. Hard.