You can rent points to stay at non-DVC resorts, but it may wind up costing more than cash through Disney. Non-DVC resorts take a LOT of points. As far as January, I would wait until you are sure you have your vacation dates firm...but you may not be able to book the exact DVC resort you want to stay at. OKW and SSR would probably have the most availability because of their size, VWL and DCV are often booked early because of location, Stormalong Bay, etc. But it never hurts to ask the DVC member to try to book thoswe resorts if they are your choice.
Book with a DVC member you feel comfortable with, look at the post counts and how they respond to others here in their posts. Remember that the DVC always has control of the ressie, but also stands to loose points if you don't fulfil your end of the contract...so there is a fair amount of trust required on both sides of the transaction.