This is my experience from Korean airlines DFW- ICN - KTM and LAX - ICN - KTM
1) Two checked in baggage (50 pound) per traveler
2) Hotel is provided one time for round trip ticket, you can choose when to use it.
3) the hotel inside the airport in Seoul is over booked all the time, make sure you book hotel early before travel and let them know when do you need hotel.
4) If you stay in hotel inside airport you do not need visa. They will put you in outside airport hotel if inside hotel has no room.
4) You need visa if you're going outside the airport, and its on arrival visa so no hassle.
by the way did you buy ticket from Korean airlines.