The problem you overlook is “hour 1” is the extent of the war. The minute actual combat begins, 30,000 artillery pieces open fire on 1/4 of SK’s population with 10,000,000 casualties minimum.
Wow, that is a bit of a stretch.
First, most of Seoul is outside of even the heavy artillery range. Second, in order to be within range, those maybe, maybe 5,000 pieces of heavy artillery must be clustered in a fairly small area just north of Seoul and further be located on the sides of the hills facing Seoul. Tac nuking or MOABing (penetrators) those hill sides would start silencing those guns very quickly.
I haven't overlooked anything. Yes, artillery would rain on Seoul's northern suburbs for a while. But only as long as we allowed it.
The Norks have nukes and have stated unequivocally their intent to use them. Hitting the sites in NK with penetrating tac nukes would be in order and would have minimal fall out on the South.