No, I think it makes most sense as being "Man first wife", ie someone who has been faithful to the wife of his youth and can set an example to the remainder of the congregation of the faithfulness that all Christians are to have to their wives, to each other, and that God has to us.
Having said that, given there is forgiveness and life is complex, that may also apply to a man who retains the wife he had at conversion even if he had divorced and remarried prior to that. It might also apply to a man who has attempted to the best of his ability to retain the wife of his youth, and in the view of the elders is not responsible for her failure to reciprocate this faithfulness. Real life is complicated, some of these things may be guidelines rather than set in stone.
But the word "first" indicates they are setting an example that is strongly encouraged elsewhere, so fits into one consistent scriptural message.
The interpretation "a" means they should be married, which is plausible but doesn't really match up with other passages.
The interpretation of "only one" or "no more than one" contradicts the general thrust of the remainder of scripture, so isn't valid in my view. And if it IS the correct interpretation, and I am wrong, God will recognise that it was quite easy to get that one wrong and won't be too harsh on those people who disobeyed through misunderstanding.
Given Paul was talking to Greeks, they only ever have 1 wife. So it likely is 'first' or 'a'. Although it could be 'one' in that he hasn't divorced and remarried several times. But 'first' would have that meaning as well.