Your income should come from a job performed legally in Thailand. Your evidence would be your tax returns (phor.ngor.dor 5).

By legal you mean with a Work Permit, I have done my tax assessments for the last 3 years, but as I work outside of Thailand and pay taxes here, therefore no WP, therefore no Citizenship.

If you work outside Thailand, why do you pay taxes in thailand? You do not need to pay taxes on your foreign sourced income.

".....if it isn't repatriated into Thailand in the year it is earned" (for those who have tax residency in thailand)

Ok got my stack of documents ready just waiting for the 2 Thai's to sign on my "good character " - I got a Lecturer and an M.R. to do this so hopefully their names will help my course! will submit everything late this week or early next. I will keep you posted about what flies,.....

No, they don't care who your witnesses are and you have to ask them their salaries to complete the forms. It will only make a difference if they have the clout and willingness to go into bat for you at the Interior Ministry. Just signing their names and walking away will make no difference at all.

April 2013 - addition of my name to wife's family tabien Baan house book

I would do this as soon as possible, and is an important thing if you plan to apply for Thai nationality without PR.

Needed for citizenship but not for PR. Most district offices will not put you in your wife's family tabien baan, assuming she and her family are Thai, because you are not entitled to be in a Thor Ror 14 (blue) tabien baan until you are a PR - Catch 22. You will probably need to apply for a Thor Ror 13 under the Civil Registration Act 2008. However, some district offices seem not to know this and might put you in the blue book.

What if one was pursuing Citizenship, but unmarried. Is it possible to become a citizen if you are single?

yes, it is possible. But in that case you must first apply for and receive Permanent Residency. So it takes longer and costs more.