I believe that if you have already sent a copy of your passport and stamp proving that you were in Vietnam to start the process there would be no problem. But there is always a risk.
If hypothetically you were able to bring this money into Thailand you would not be taxed. But just to be clear, so far the tax on money for those who stay more than 180 days in Thailand has not been confirmed.
I don't think that would be a problem. If it happened the way you're telling us, I highly doubt he would take it that far. But then you said you were here for over 20 days... Did that all happen on the same trip? Because that could be a problem... You could go to the Thai Embassy and ask them.