NK is playing for keeps and they will batter the hell out of whoever makes a move on them.
52,000 sounds about right for a conventional war. However, why we would need boots on the ground is beyond me. That's SK's job.
Make no mistake, the NORK's would give China a damned good blood letting.
Your post is correct, the NORKs do have a huge, capable military. But in a sustained war with a big industrial nation, (U.S., China), their weakness would surface and they'd be in deep trouble; that being a severe lack of supplies, re-armaments, food, spare parts, ammuniton, etc.