Base: 10 = exactly what it says, it's the base size.
Leadership: 20 = you get an increase of 5 for each point of the leadership skill you have.
Charisma: 12 = you get an increase of 1 for each point of the charisma attribute you have.
Renown: 2 = in Mount and Blade: Warband you got an increase of 1 for each 25 renown you have, I don't know if it's the exact same amount of renown required in Mount and Blade: With Fire and Sword.
Total: 128