I'm just gonna comment this here for my hypothesis of why he needs so much money..... I guess he needs it for the families of his subordinates which probably died because of his orders..... one of my evidence is what the gold bug said about him, saying "he was carrying 30000 people's lives behind him" or something like that.... and also judging from his encounter with his alleged former subordinate, I think I about 60% sure of this.... I'll update this if I'm wrong, or I'll just comment on the chapter where I find the answer.
Edit: okay, so I just read the rest of the chapter and I seem to be 70% correct, He was sending money for a tribe he destroyed and not for his subordinate's families.