You can have some of them not completed yet, but if I were you I would complete as many of them as I can, and leave just a little for the last year. But yeah, you can pretty much apply whenever you want as long as you have the requirements fulfilled by time of matriculation.
I don't know about what kind of chances you will have to get int dent school compared to someone who has already finished the requirements and more then that, but yeah, you can apply. Hope that helps.
george