I need help to modify my Savage

Hi guys,

I'm new of this forum and I'm very interested to modify my Savage with a BL motor but I don't know from where to begin.
I have these materials:
Savage 21
Warrior 9920 Brushless Car Controller
Lehner Basic 4200 brushless motor
14 cells 3300
Now:
which are the connections between battery and controller?
I would want mantein the stock 2nd gear. is possible? or I must modify it with eavy 2nd gear?
which other modifications I would have to make?

I hope that someone can help me

THKS