The monthly income method definitely requires the funds to be identifiably deposited from a foreign source. However, they don't inquire as to the origin of the funds for the banked money method. Just show you have the 800,000 baht in a Thai bank for the requisite period of time.
Also, it depends on what Immigration office you are reporting to. CW in Bangkok doesn't ask to see a bankbook at any time until you apply for an extension.
If was to go back for an O-A visa I would just get one here in case I had problems in the US. It probably costs next to nothing and there is nothing wrong with having too much documentation. Good idea.
I believe Bangkok Expats or Bangkok Informed has organized with several different sections like real estate, jobs, etc. it concentrates certain topics to sections and frees up the main discussion thread. You would have to talk to the moderator to ask how successful it is.