You can subpoena the doctor without compensating him/her for the time, but you will not have a very cooperative witness. Usually, the doctor is not called but the records are subpoenaed and placed into evidence.
There is a big difference between subsection b and c. Subsection b is a violation, not a crime, and subsection c is a criminal misdemeanor. If you were given a ticket for subsection b, you can either pay the fine or go to the hearing and try to get it reduced. You really do not need a lwayer for this. The charge will not be changed to subsection c and nothing will appear on your record.
Probable cause is needed but may have been from the observations of erratic driving. You should be able to tell this from the criminal court complaint. Speak to the lawyer about getting a copy of the complaint. Sometimes, there is a traffic violation that was the basis for the stop but no ticket is given on the theory that the DUI is a more significant issue. This, however, is not a good practice from the prosecution's view because it does raise an issue about the validity of the stop.
You should first ask permission from probation. If they say no, either your original attorney or a new attorney will have to make a motion before the judge. If the wedding is at a location where most of the family resides, and that can be proved, the judge might allow it.