1. It really ranges. 3.5 is the number I see here to be considered competitive, but people get in all the time with 3.2-3.5. It's pretty rare if someone under 3.2 gets in, but it does happen.
2. Depends on the individual. However long you need to study to get good grades. Personally I don't kill myself studying and I have a good GPA, but there are people out there who study 4-5 hours everyday. If you're talking about the DAT, usually people study a few months in advance. It's best to apply summer of your junior year and the earlier the better(applications open around June-July I think.)
3. Useful if you need motivation to study, but if you can study fine on your own its usually a waste of time/money. You'll hear mixed reviews, but from reading here if you spend about $500 on a few resources(check the DAT forum and read some breakdowns), you'll get off a whole lot cheaper and be more effective.
4. Whatever you are interested in. Volunteering looks good, but you need to make it something you are passionate about. Any pre-dental/pre-med clubs look good too, but try to get a leadership role in them rather than just being a member. Join a fraternity/sorority if that's your thing and get involved in leadership there. And you'll need to spend a decent amount of time shadowing a dentist(50 hours min, you probably want to shoot for around 100).
Hope that helps
Sorry, I thought you said GPA instead of DAT.
