An officetel is just a small apartment. lots of escorts host out of them, sometimes clustered together in the same building.
As to KissBang -
first off Bang is Korean for room. A Kissbang is a store front that has a bunch of rooms. where i've been they have women in their early 20's as hostesses. you pick a girl you like (or maybe 2) and go in to a room. From their it is somewhat up to you and the girls willingness what happens.
At a minimum for me its been DFK, girl naked from the waist up, and a HJ. No massage. I've had acquaintances complain about the girl making the guy finish by himself, but never encountered that myself. At a maximum I've been offered FS there. The norm for me was CBJ. You can think like the kissing and self-pleasure is part of the base fee and the rest is negotiable with the girl.
Kissbangs are not really my thing, havent been to one in 10 years. I was not aware they all closed in Seoul. there used to be hundreds of them all over. Its more of a young guy thing after a bar, after work with a bunch of other guys to go. The girls are pretty enough, but the ones i went to never let you plan ahead for a specific girl.