Flying on the newest 3-class 777 from Saigon to Incheon? Seat 3K is fine, but I'd rather take 4A or 4K. You sit closer to the window and it feels that much more private being away from the aisle. There may not be much to see out the window during the night, but during landing there might be a nice view. Granted you are a bit closer to the bathroom, but usually during those late night flights most people tend to sleep. As for Seat 2K on OZ222, sitting up in first class? Enjoy! I would certainly try the Bibimbap korean food choice, if you've never tried it on Asiana before.

As for lounges at ICN, your only choice will be the Asiana lounge at the main terminal. There is no reason to go to the concourse terminal as all Asiana flights are out of the main terminal. Just a heads up, the food choices at the Business class lounge can be a bit lacking. Since you have seat 2K for OZ222, I'm wondering if you will get first class lounge access.