From what I can tell, selecting seats is not a big thing for the Korean passengers. There were a lot of unassigned seats on my flights at T-24, but they were occupied upon departure. At T-30, you should have your choice of seats (or an equivalent one, I did need to take a window seat on the right side rather than the left side on one flight, but in the same row). ICN also has dual jetways at every single gate, from what I could tell, so disembarkation is pretty easy. Probably a bit slower from the A380, but should still be very reasonable.