So, just wanted to give some general feedback on my visit to Samui immigration. I went prepared and had all the copies of documents and photos needed for extension. We both dressed appropriately (though many westerners did not). We arrived at 10.30, queued 30 mins and were asked to come back at 2.00pm. ( we headed straight to the beach and chilled out).
Our numbers were called at 2.35 and we were on our way. It was very busy, very efficient and made very easy to plan for, thanks to your advice. Cheers!