1) You could, but it wouldn't affect your charges. It's not retroactive.
2) You should definitely speak with an attorney.
3) See 1.
4) Yup. Sometimes it takes time to get a court date.
5) If your record is not automatically sealed when you reach the age of 21, you may petition the court to have it sealed.
6) Apply for a hardship license and see what the DMV says about it.
7) Forget it. The field sobriety tests were not administered illegally.

As far as your Miranda rights, they were not violated. Miranda applies when you're being taken into custody and interrogated. You were not taken into custody.