I'm not quite sure all SAMs absolutely must be eliminated in a first strike.
Ballistic launchers, guns, and maybe airbases can be all used to attack Seoul or other targets of value. SAMs are threat to aircraft, but one cannot attack Seoul with SAMs. So they can probably be put off till after stealth aircraft deals with ballistic missiles, and you can probably use regular HARMs against them. Also sub bases can probably be attacked with TLAMs. I don't think North Korea has missile-capable submarines (?), so there is no risk of them just driving outside their pens and firing at you. You can probably pre-arrange submarine patrols to intercept most of them as they disperse from their bases.
So if I understand you correctly the first strike hit list by stealth aircraft will consist of:
- 10 nuclear missiles
- 1.000 ballistic missiles
- 500 artillery and MRL's in reach of Seoul
And then a followup attack by conventional aircraft will deal with:
- Enemy aircraft
- Highways, railways going to south
- Headquarters, communicationcenters, electricity production
And submarines will deal with enemy submarines leaving their bases.
The risk of their submarines is not that they are going to fire at you, but that they are going to drop special forces behind South Korean lines, which I think is a serious legitimate fear. They have done this in the past, and those special forces were pretty good at spreading chaos and destruction. If I remember correctly they almost fought their way into the presidents residence.