But!!!! Its up to the officer at the border if he belives your a tourist or mis using visa rules its all about previos stamps in your passport so no one knows
Getting extension when in the country is no problem
Your problem might be getting in the country, many airlines demand you have a return ticket or forward ticket within the 30 day on arrival visa before the check you in at the airport
it is not 6 month anymore no they want 12 month and offcource the bank can only give you 12 month via their headoffice in Bangkok so this takes 7 days to do