I'll just speculate and express my fears without having much knowledge of the subject, simply because what's going on has the obvious potential to affect the lives of basically every living beings on this planet for coming decades (if not generations to come) if it ever goes to extremes.
So, I won't pretend to fully understand how it would 'go down' like, but it sure as heck would be ugly. It'd be war, with massive scale destruction involved (well, that's the obvious part). We really don't need to analyze much on this subject. Even if the war is exclusively fought with conventional weaponry, just those North Korean artillery cannons aimed at Seoul would cause enough carnage, tens of thousands would die in South Korea. Then, there's the poor population in North Korea, outside the military, in the rural regions. Those innocents are poor, hungry and rely on eating grass, tree bark and rodents to survive. How in the great heck would they endure a war even if it's focused on and around Pyongyang? What would be the direct and indirect consequences on the millions living (rather, surviving) in North Korea? It might result in a massive post-war exodus... to where? To a possibly devastated northern region of South Korea? Seeking shelter north to China?
How about the amount of resources and logistics necessary for the post-war monitoring of the remnants of the North Korea regime to ensure no attempts at future retaliation? What about the reconstruction efforts? How much of the U.S. military will have to stay there and for how long? Will the remaining population have to live under martial law? Just to think about all of what 'might' happen, and how it would go down like makes me want to puke. There's absolutely nothing good for nobody coming out of a potential war over there.
But, ultimately, from what I think I understand is that Kim wants to provoke the U.S. (well, Trump) to fire the first shots (figuratively and literally speaking). I think that Kim probably believes that Trump, contrarily to Obama, is more susceptible to act impulsively; and because of that ever since Trump came to power Kim significantly increased the verbal provocations and the missile tests / launches. If Trump and his military advisers sort of 'fall for it', and do make a 'preemptive' strike... then I think that it would give a good reason for China to step in, in favor and defense of North Korea. In my mind, that's the biggest danger. I do think that we (the U.S. and its allies) can deal with "just" North Korea, if they're alone in the war. But if China perceives a would-be preemptive strike as nearly a threat to them as well then we're in for quite the fireworks, and it won't stay regional very long. Then, worst case scenario... what if Russia steps in to give a hand to China too? Yeah... I did say worst case scenario (that would go global and that would definitely become a definitive World War, most likely nuclear, and wouldn't last very long).
The 'best' case scenario is that Kim loses patience, that the U.S. doesn't fall for the trap and they (the North Korean regime) fires the first shot. If they do that, it gives legitimacy to the U.S. and South Korea (and other allies if they participate) to act defensively and go in without the intervention of China. It's the 'best' case scenario for the planet, but not the for region and certainly not for the South AND the North Koreans. There will be massive deaths on both sides regardless of how the U.S. military would be efficient versus the NK's. All the North Koreans need is a decent distraction, sending fake 'nuke' launches and let the interception defense systems get one or two of them and then launch the real ones to increase chances at actually hitting one or more targets (Seoul, most likely).
Bah... anyway. I don't know how it'd go down tactically and logistically speaking. But it'd be ugly, and it would impact the entire world's economy for coming years. It might also break economical ties between the U.S. and China, etc. It'd be a modern war on a scale that we would have frankly never quite seen since WW2.
