Daughter's orthodontic treatment

My youngest daughter has straight teeth, but one of her front teeth is slightly crooked. I want to get braces because it looks unpleasant.

I am currently in 5th grade. When would be a good time for you to do it?

I have only one front tooth that is misaligned. Should I proceed with partial orthodontic treatment? Or do I need to have the entire set corrected?

I've heard that orthodontics can lead to more cavities. Is that really true? I don't have any cavities right now, and I'm worried that focusing on aesthetics might cause more harm than good.