Incheon airport is located on an island, so to get to it is going to take a little longer than it would take to travel to Gimpo for example. There are a few different options to get to Incheon, some people get a bus directly. This can take between 40mins to 1 hour plus, depending on where you live. Other people drive/get a bus/train to Gimpo then take the bus from there. This takes 35 minutes.
The standard of apartments is high. The company however are trying to locate the expats outside of the city due to the expense. By "outside of the city" I mean, 20-30 minutes from the city centre so not bad.
Like in most places, if you want a car, you buy a car. It makes life easier. Most people I know have one, it is not necessary though.
"walking one km to get food"..... I doubt it.
Hope this helps