Please, I want to know if one can use the church's money in his custody to run his personal business.
Absolutely not. The money is the Lord's money. When Ananias gave money to the church, but lied about the amount, Peter told him: "While it remained, was it not your own? And after it was sold, was it not in your own control? Why have you conceived this thing in your heart? You have not lied to men but to God" (Acts 5:4). Once funds go into the collection it becomes God's and can only be used in ways that God authorizes.