North Korea, on the other hand, has enough artillery on the border to
completely level Seoul within a few hours, from what I understand. That
alone is enough to stop any plans for an invasion. In a way, it's even
worse than the nuclear problem. Unlike a nuke and its delivery system,
there's no possible way to take out mumble-thousand pieces of artillery
before the deed has been done.

Kinda makes you wonder how well they can coordinate those artillery
pieces... they can't even feed their troops.

Actually their army get's fair chunk of the food, it's the civvies that are
having the worst. So the question would be "How much fuel does the army
have?"

Out of the tens of thousands of cannons sitting on the north side of the
border, anyone want to bet that no more than a couple of hundred
actually get to fire? Especially with a few dozen MLRS launchers and a
couple of hundred attack aircraft cranking out a few million
submunitions across their firing positions... while reducing their
command centers to smoking holes in the ground and jamming
communications.

Koreans have had time to prepare firing positions for their artillery, so
they should have some cover. And using landlines reduces the risk of jamming
and can provide quite secure communications if they have enough of "surplus"
capacity.
But I don't think that that many NK artillery pieces can reach Seoul from
their prepared positions. What is the howitzer/cannon ratio of NK army? And
I doubt that they have newer shells with longer range.

For reference, look at the "massive" weapons infrastructure in Iraq, and
how they never managed to get more than a few percent of them into play.
And Iraq was in relatively good shape compared to what Korea's going
through right now.

You have to take notice of cultural differences. Korean mentality is quite
different from arab mentality.
But it is true that NK wouldn't be able to beat SK, but it might inflict
some really nasty damage to civilians, specially if they can lob chemical
weapons with their artillery and missiles. And if they have working nuke
with delivery method, it can turn quite nasty.