You are incorrect that "they could [sic] give a shit" (you probably meant couldn't) about wealthy Chinese citizens. With affluence comes influence. Maybe if we were talking about factory labourers they would not care, but when a country's wealthiest citizens are in mortal peril you can bet your ass there will a swift response.
You are correct that trade relations are key here, and I omitted this 800 pound gorilla. Thank you for the addition.
When its war, they aren't going to sacrifice any intelligence/surprise advantage to preserve a few tourists, that is true for either side (PRC, ROK, DPRK, USA). It doesn't matter who these citizens are actually, and its probably not the "country's wealthiest citizens," those are either safely at home or in Hong Kong. We are talking just about a few rich business men at most.
The situation is not so delicate that China would be able to brush off these deaths for strategic reasons. I'm not even sure what you think a strategic reason for China biding it's time would be. A vague reference to intelligence/surprise attack doesn't really mean anything. A rapid response from the north is an automatic loss for North Korea, there will be no waiting.
There would be no wait actually. If DPRK warned the PRC that they were really going to attack, the PRC would just invade DPRK immediately, they might warn their tourists but this is only a secondary thought.
You are correct that trade relations are key here, and I omitted this 800 pound gorilla. Thank you for the addition.