I believe that if you put 1/2 down and plan to pay it off in a year, it's 4.95%. Otherwise you can put 20% down (and part of that can be the $10 discount they are currently offering) and the rate will be 9.75 with terms of up to 10 years.
There is no guaranty that they will still have the incentive in place in a couple of weeks. If they do still have the incentive AND you take the tour, you have 3 days from the end of your vacation to call
DVC and get the incentive.
My advice is this:
If you have alternative ways to finance, look at resales. You can pick up an OKW contract, sometimes with banked points for about $75 plus closing costs, which would make your real costs about $77-78 pp. Plus OKW has the lowest mainenance fees. You could also pick up a Hilton Head contract for $5 pp cheaper, but you wouldn't be able to book at WDW until 7 months out. HH has the 3rd lowest dues after OKW & SSR.
The drawback to resales is that SSR has 12 more years than the others plus withg resale, you have to go through the Right of First Refusal process.
If you are dead set on SSR, go ahead and contact DVC and ask them to send you a contract NOW while you know the incentives are still in place. You have up to 60 days to sign before Disney cancels it plus 15 more days right of recision once you sign and send back. If after your trip, you decide that you want fewer or more points, DVC will adjust your contract and still give you the incentive on all the points you buy. Plus you still don't have any payments until May.
Or you could do the hybrid approach. Get a contract from DVC. While you have the time to sign, keep checking the resale market to see if you find a resale you like.