Can I take Advil (ibuprofen) while taking vicodin after root canal therapy?

Sure. Multimodal therapy is very effective for acute pain. Advil 800 mg every 8 hours for a few days can be taken independent of vicodin dosing. As the pain improves consider replacing the vicodin with plain tylenol (acetaminophen) 625 mg every 6 hours. Try to avoid taking tylenol (acetaminophen) and vicodin at the same time as vicodin also contains tylenol (acetaminophen). Max daily tylenol (acetaminophen) should not exceed 4 grams.
Yes. The two medications you listed are often used together to treat pain as they each have a different mechanism of reducing pain.
Mostly yes.... Yes, but raher increase the dose of vicodin. It is much stronger than advil (ibuprofen).