Yes but rarely. Depends on many factors like location of injury force age of person and underlying or coexisting medical problems.
Not commonly. A simple concussion, without significant structural damage to the brain, is less likely to lead to post-traumatic epilepsy than a major head injury.
Not commonly but yes. Seizures are occasionally associated with more severe concussions. However, one can not assume that a concussion is the cause of a seizure. Further work up for the cause of a seizure should occur and may include a ct/mri of the brain, an eeg and a consult with a neurologist.