Pretty sure Patong don’t do 30 day extensions anymore. They were only doing 7 day extensions last time I tried. I had to go to Phuket Town immigration.
You will need your TM30 from your hotel or landlord, just ask them and they should know. You will need to make some photocopies but that can be done at the immigration centre, it’s located at the back. Copy people know what you need to copy, costs a few pennies/baht. The forms you need to fill are supplied at reception of immigration. They close for lunch between 12:00-1:00. Either go early, when they open or go at 1:00.
it’s not about showing you have a job or income coming in. It’s all about the money amount you’re sending into Thailand, each month. For marriage visa, you need to show Thai bank statements showing 40k a month coming in.