First of all to the uninformed REP is an airport within the Border agreements of Thailand so no need for the waffle on paying taxes. its already in your ticket. ( see point 4 below ) ( Thanks halibahs must learn not to type so fast and press send ) YOu are actually only a transit passenger which is what BKK built its huge growth on during the late 1990's as a transit hub into Asia.

Secondly where CX park and where you depart is about 20 minutes walking via security / passport control. You cant go wrong its so easy to find.

Once you get the Bangkok Airway area its all set aside for their flights and they have a lounge you can use as part of the ticket, nothing special but better than hovering like bees around the honey pot waiting to board.

When you arrive in REM they will have your name on a board and you clear immigration there. You will be given a sticker to put on your shirt to ID you as needing to clear passport control on arrival in REP.