You can reschedule or just go late to the biometrics appointment. It should not be a problem. As far as this incident, yes, if he is convicted, he could be deported from the U.S. They would give him an interview, but they would deny him at that point. So you have to hope that he can avoid a conviction. Make sure your attorney knows that a Withhold of Adjudication still counts as a conviction for immigration purposes.
It is not a character test. It is a marriage interview where you have to primarily prove your marriage. Secondarily, they will want to see that he is not a bad person. If this is the only problem he has, it should not be a denial if he is not convicted. Yes, he should receive his EAD before his interview regardless of the criminal charges.
Factors are experience in criminal law and experience in immigration law and the combination of the two. That is not too young, I don't think. 6 years is a good amount of experience, just make sure he has experience in the right areas. If he doesn't have much immigration law experience, or at least good knowledge of the immigration consequences of criminal activity, then you will need to find someone else. You can also look at www.ailalawyer.com.
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