Lawyer? Unnecessary

A lawyer is not necessay in your case. However, you must make sure your additional evidence, the way you present your evidence and the way you argue must be strong enough. Remember, what the INS officer wants to know from you now is your ability and past track of achievements support your future contribution will substantially greater than an available worker with minimal qualification. You have 28 papers and you are a professor, you have ability to write this letter. If you are not sure, I recommend you to post your letter on this web to ask opinion before you submit it. Good luck!