Congratulations Mr. Moon as new president of South Korea. So you want to start something fresh on your foreign policy. Here's my two cents:
1. South Korea is a vassal of the America Empire. As such, you have no independent foreign policy. Well you can try but you will end up like North Korea. 
2. Yes please go to China. You can talk and talk. And they will listen and listen. Nothing will happen. Until you demonstrate you dare to conduct an independent foreign policy. And survive the CIA. 
3. Sure go to see Trump. He will lecture you about everything. He will demand $1 billion payment for THAAD. You pay up, you go home. And wait for his instructions. 
4. By all means go to North Korea and meet dear brother KimJ. You can talk old times when Korea was a single country. Until the Japs arrived. And until the Yanks arrived. KimJ will ask you to tame the madness from the Empire. Oh the nukes. That's to make sure KimJ won't end up like Saddam. After all, both Mad Dogs are over there.