Like North Korea are a bunch of innocent boy scouts? Just because the US does dirty stuff doesn't mean that all dirty stuff is per force carried out by the US.
It seems that you are putting your conclusions ahead of the few known facts.
They are developing a nuclear weapon and have the fifth largest army in the world (even if it is not the most modern). They also have limited support of China. Most of the peole may be poor in this country, but I would not considered North Korea as a state with limited means.
No, it's just a third world country, with limited means.
The military budget of North Korea is estimated to be around $10 billion USD. It has a million active troops, 6,600 tanks, 700 MLRS, 460 fighters, and so on.
The country is perilously poor. Many people starve. But the means are there for an operation like this, especially if sponsoring foreign groups, if the motivations allow.
And to counter the growing narrative that the NK thing came out of nowhere as a convenient excuse -- the country was very offended by this movie six months+ ago, long before the hack, to the point of threatening military retaliation if it was released. Engaging in or hiring hacking groups to put the pain to Sony seems entirely within the realm of the possible, though threatening actual terrorism is a bridge too far, and overplayed their hands if they were involved with that.
The budget figure is probably BS. Their whole GDP is about 12 billion USD in toto -- and they give around 10-15% of state expenditure to the military budget (the peak was 30%, according to wikipedia, back in the seventies).
But even that figure ($10b) is comparable to places like The Netherlands, Quatar or Poland (hardly forces to be reckoned with), and 1/3 of what South Korea spends:
All military figures are BS. North Korea has 1,000,000 active member troops. Canada has 68,000 active member troops.
North Korea has more of everything than Canada, including aircraft, boats, and even nuclear weapons.
Canada spends $23 billion per year.
And as to forces hardly to be reckoned with, if you're talking in a convention war with the US or something, sure. To put that into contrast with hacking Sony, though, is utterly ludicrous. The latter could likely be achieved paying a group less than it costs to operate a single fighter aircraft for a year.
While North Korea does have enough capacity for trouble, your figure of "6,600 tanks" etc. should be taken with a big grain of salt. Those tanks are ancient.
It seems that you are putting your conclusions ahead of the few known facts.