Would character letters help with trying to get a felony conviction expunged in Tennessee?

You can't just call up a lawyer and get a free answer to this over the phone. They need to see your records, what the felony was, how the sentence was carried out, etc. If you do not have the money to hire an attorney, contact the Legal Aid office in your county. Just do a search to get the address and phone number (like "legal aid" +"Jackson County" +TN).