Questions, if I understand this.

I think the new rules is that you or you wife(thai) ot together, must have 40.000bath montly income, right?

Your thaiwife must go to gouvement to registrate income, 40.000baht and pay taxes for it, correct?

How much must she pay in tax? (maybe it depend of what she do, ex. minimarket or lunchrestaurang or other)

thanks a lot

To get a visa and to extend one is something different.

New rules for extension, "old" rules to get one. If I understand the headline of your post correct, you want to get one.

As far as I know you just need a marriage certificate if you apply for a non o visa in your home country (at least that's the case in Germany.)

He appears to be asking about a one year extension of stay from immigration and yes the new rule is 40k family income. Thai income will have to be confirmed by tax receipts for 3 months. I don't know how much your wife would be paying in tax but the rates are really not that high here.