Factors that make Zakaat compulsory

Zakaat on debts

Q: I borrowed some money from my mother to buy a car. We used that money to pay for the car and I will be paying her back every month. Will zakaat have to be paid on that amount if it is already used in buying the car? 

Wealthy Muslims taking loans from the bank

Q: In our time, there are wealthy Muslims to take out loans from the bank for tens of millions of rands for the purpose of business, e.g. constructing an apartment block. Or taking out a mortgage for buying a home. Please advise:

(1) If the amount loaned exceeds their Zakaat asset value, does that mean these Muslims do not have to pay Zakaat, and that they are also eligible to receive Zakaat?

(2) Likewise, is it better for them to use money to pay off debts or Nafl Sadaqah/Lillah projects?