Balayage question

Hi guys,

I'm new and i'm hoping someone can help me....
I have been bleaching my hair balayage style with normal box bleach for a while and now want to try with professional products. My hair is naturally chocolate brown.
I've got some well a colour charm t11 and understand that I need to mix this with developer (I was thinking 20).
My question is: I only want to lighten the very tips of my hair this time, do I A. Have to rebleach the ends or can I just put the toner/developer on? And B. If I do need to rebleach the ends do I put the toner/developer over the rest of my hair to help blend it in?

Can anyone recommend a powder bleach and developer?

Any advice would be greatly received.

Carla