How much money is enough and how do they ask you to prove it

Hi guys....

We are busy filling in our forms for the 176 family sponsored visa and they ask how much money are we planing on bringing with us to Oz? What must we put, I know that sounds strange but how much is enough. Realistically £15kis what will we will have left over once we sell our house, is that enough?
And also they say that they may ask you to proove this .... how? Is the papers showing we own a house and car enough? Or our payslips? Or does it literally have to be £15 000 in cash sitting in a bank account somewhere?

I keep hearing conflicting stories.... some people say I wont have to proove funds for a 176 family sponsored visa and others say I will have to prove $35 k in cash .....

Thanks guys.