Side effects with amiodarone are very dependent on the dose. The lower doses used for atrial fibrillation are much less likely to lead to side effects, while the higher doses used for ventricular arrhythmias are much more likely to lead to side effects, especially with long-term use.
No effect on coumadin levels with the flu vaccine that I know of.
The flu shot does not cause the flu. You can still get the flu after the vaccine though. If you are having breathing or arrhythmia problems, you should see your doctor.