My post was just a reminder to check for other immigration papers that may be needed, best to get all you might need while there.
Re the REP, I never had any intention of leaving Thailand, but a few years ago I had a family emergency, I did not have a REP and eventually got one at the airport. Inevitably there were problems and I nearly missed my flight.
Getting a REP while doing a 1-year extension could save you a lot of hassle.