Real threats for China is SCS
Japan, South Korea, Singapore maybe Indonesia?
Rest everyone is weak and none needs more than subs, frigates and destroyers
None of them are threats to China, China just want to make sure countries in their region will not win any conflict if China want to do some sort of aggressive move.
Singapore is far away from SCS and their location is protected by Indonesian large sea territory in Riau Islands province that also include Natuna islands. They dont like to make a war due to small population, doesnt have strategic dept and also they dont produce food by themselves and rely water supply from Malaysia. Sabotaging the water pipe supply from Malaysia will be enough to make them very nervous.
Their military build up is meant for defense purposes, particularly intended to Indonesia. China is not a threat for them, you can see Singaporean PDF members cozy relationship with Chinese member here and their support on China expansion in SCS.
Understanding China agressivenes in SCS
Talking about China. Chinese in China mainland have been indoctrined that SCS belongs to them. Their school, history book teach them to believe like that. When they were weak and poor, they dont make any aggressive move, but when they are strong we have seen a different story.
Psychologically, their leadership will always get pressured from their public to make something in SCS. As I said they all believe that the region belongs to them. It is difficult to let go past indoctrinized, particularly to let go something that is said as yours by your elderly. Even religion like Islam get difficulty to change people previous belief that is made by their ancestors. People tend to stick to belief that was hold by the society for such a long period even though it is false according to current logic (international law).
Even Indonesia doesnt release East Timor despite we clearly invaded the region and we just release it after we face both severe economic problem due to Asian Financial Crisis and Western political pressure. For your information, Indonesian people under Soeharto regime get indoctrinized that main party in East Timor want Indonesian military to come to fight against communist Fretilin which become their rival.
This is the simple logic to understand our policy at that time. We rely the loan from IMF to escape economic crisis and the countries who provided the money want us to let go our occupation there. So better we let East Timor to have referendum and leave Indonesia rather than we have to face economic difficulty that will affect whole of our people.
If we dont face economic difficulty, we will likely to continue our colonization in that country. I bring this to give some sort of perspective that indoctrinized can effect government policy and we only can escape the indoctrinized when we face bigger threat.
Going back to present. China will not target Japan and South Korea. Both of them dont have anything to do with SCS region. China just want to make sure countries such as Philippine, Vietnam, Malaysia, and Brunei will not challenge its present in SCS. China will do that step by step. As for Indonesia, I believe China will likely to avoid any confrontation with us due to geopolitical and economic reason.