I guess you dont need to make full payment. You can book your car with 500,000 amount.
As far as safety is concerned, you'll be making payment to Toyota showroom, and they will definitely give you some receipt etc, so its safe. Make sure the delivery time is December on the booking order, as they have committed verbally.
I paid my full payment for Altis 1.6 4 months before delivery to toyota ravi, Lahore. No problems.