When you rent points you are renting from an individual owner. Each owner will have his or her own way of doing business. There is no standard way of doing it. If you don't like the terms one owner is offering, you can try another.
Depends. Each owner may have their own way they like to handle reservation payment or payments and as always mentioned on these boards you'd best have a contract ( definitely read the stickies at top of Rent/Trade board for important info/advice )
But it seems majority want to be paid in full so be prepared to be fully committed to the dates/number & type of rooms you want & have full payment ready at hand.
For those owners that take a partial payment they will expect the balance of the payment on the date they indicate or you can expect the reservation to be cancelled; especially if close to 31 days before the check-in date since an owner will not want their points that they will use for your reservation to go into holding status with less than 31 days to go.
Another IMPORTANT detail for you to know would be what is the owner's policy on CANCELLATION/REFUND IF ANY. Many will have a no refund policy if you need to cancel, some may refund some of your money depending on date of cancellation, some may only refund money if they can re-rent the reservation.