I buy things online all the time, and haven't had a problem yet. And if someone were to steal your #, most credit cards would protect you from any damages.
I think tickets are going to go on pre-sale like a month before the movie opens. Some theaters will let you print out the tickets at home, and then they just scan it at the theater! 🙂
I'll just wait a couple of days and see it on the next Tuesday after it opens.