We tried doing it ourselves we got all the paperwork done that was the easy part ( not ) we tried 4 times at different marriage offices all needed a witness and or translators, my wife’s parents etc etc we used an agent eventually at a cost of 5,000 baht to actually get married at the office. Ministry of foreign affairs Bangkok where you go to get your information verified plenty of agents there. I always try to do things without an agent but this time it was useful.
Yes 2 copies of everything required, I visit my immigration 2 weeks before renewal to get my paperwork checked and ask if they need anymore information before the due day.
It is worth the hassle but 1st year 6 visits to immigration 2nd year 4 visits this year hope for only 2 but who knows.