Once you know the documents needed it's relatively straightforward. The problem with hive minds is your gonna get everyone's 'opinion'. The only way to get right information is to go to your local immigration office find the person that deals with the type of visa you want and ask them to give you a list of their requirements. Ask specific questions until you get specific answers.
Re my comment about random documents, went today and they couldn't find any issues with any of my documents as per the list. So they sent me to get 2 copies of my receipt....
If you are applying in Thailand contact your local immigration office. Be very specific about the type of non o visa you want. Each office appears to have slightly different requirements. This is from Phuket town immigration on Friday. Slightly different from Patong. Have no expectations that you will get your visa on the first visit. Inevitably they will ask for some random document that they haven't asked for before. Try and be patient, not easy I know. Don't argue, a waste of your time and energy you won't win.