First I would head over to the rent/trade board here at the Dis and read the sticky's at the top. A lot of your questions will probably be answered there. Also if you do a search within the
DVC boards you will find examples of the different rental agreements that owners use.
The member would make the ressies in your name and send you the confirmation in the mail. The member keeps total control of the reservation though. This is where your trust comes into play because the member could cancel your reservation. However, you can check on your reservation and confirm with member services that your reservation is in place at any time.
The member renting to you also has to have some trust that you will not cancel on them. There are cancellation policies that DVC members have to follow as well as banking deadlines that if not followed could cost the member the pts that you were going to use.
Most owners will supply a contract. The specifics of the contract as far as cancellation, payments, etc., will be different from owner to owner.
All of these details will be worked out between you and the owner until mutually agreed upon and understood.
Check the top of this board for a pt schedule so you can figure out how many pts you will need and then multiply that by $10-$12 a pt to figure your total cost estimate. There will be no room tax added so that will be your final figure.