We rented DVC points this summer. Paula you have it right, ADR's can be made at the same time regardless of dining plan or not. When staying DVC, you do have to declare your intention of doing the dining plan before checking in (like at least a week maybe) but you don't pay for it until you arrive.
Keep in mind Paula, from my understanding, they have people through DVC who can make your ADR's for you so you don't have to go through Disney Dining. I don't know if you can call them before the 90 day window and they can get you in when the time comes? That may only be an advantage for the really hard to come by ADR's (Kyle is planning on dining with Cindy at her castle right?) but worth looking into
Yes the DVC members services can book alot of that for you. The different stuff I've read on the DVC threads indicate that it is sometimes better to do it on your own...though I haven't quite grasped why???