I am not sure if you can/will be able to get a "normal" Contemporary room on points (past this year) because once a
DVC section is added to a Deluxe resort (i.e. BLT being added to Contemp) they stop allowing DVC members to "trade out" to the cash side..
Even if it is possible, "trading out" to a non-DVC unit is an expensive way to go. 1st, there is a $95 exchange fee (plus your points rental..), 2nd the points needed to stay in a normal deluxe room is usually about the same points you can stay in a much, much larger DVC 1BR with King bedroom, whirlpool tub, full kitchen/dining room. 3rd, "trading out" makes the points used, reallt restriced. changes or cancellations are super restriced and every/any change results in another $95 fee. I am not sure if it is legal for an owner to rent a trade out (inbound RCI exchanges cannot be rented), but if it is legal, I'd imagine an owner would want 100% deposit at booking
Trading out to a non-DVC is an option that might be OK for an owner that really, really wants to stay one time in the GF or Poly, just to check it out, or because you have other family there (and you want to be near) but not reallt a cost effective use of points...
2nd question.
If you need more DVC points for a DVC stay, you can add on additional 100% cash days, but each night needs to be 100% cash or 100% points. The cash rooms should be added through DVC Member services (through the member) as MS can link the points and cash nights together to guarantee you do not have to switch rooms (as might happen if you called CRO to add on cash nights, but CRO sometimes has beter deals...)
FYI, you do not actually rent "points". If you are not a member, you never have control of the points. You can rent a reservation that an owner with points reserved...