Nightlife would be a priority. I figure I can check into the hotel by 7 p.m. and the flight out is around 10 am

How long would the transit time be?

Would the hotels offer shuttles (minimal fee?)

Thanks again for the quick replies.

If nightlife is a priority, consider a hotel in Kangnam (the southern part of Seoul, home to about half the international hotels), as evening inbound and morning outbound traffic between Kangnam and Incheon is light, making for relatively predictable transit times.