If you can't get a through flight YVR-SIN or v-v, consider splitting up the flight. The ICN-SIN leg seems to be popular as it's the "first" evening flight. However, there is another 777 that flies ICN-SIN about 1/2 hr later that is less popular. Similarly, there are 2-3 flights that leave SIN for ICN before the flight to YVR.
Deplaning at SEL was mandatory for security reasons. I don't know if it's so ar ICN.