I can understand your concern and I would probably be freaking out a little bit too. But, if you review the Vacation Strategy Timeline thread, you will see that there are hundreds of posters that have had the same concerns. And, it always works out in the end for them.
Vacation Strategy is a "middle man" and they confirm the reservation through your final payment once the owner of the points releases the points to them. Some owners sell them at the last minute. And, if you have multiple reservations linked together (more than 7 days, other than Fri-Fri), they are working with multiple owners.
I am using VS for a trip in Jan/Feb and I frequently read the thread. I have NEVER heard of someone being ripped off by them. Never. And, in fact, many posters report that they are upgraded to a larger room or a presidential. I would bet that within a few days you're going to be posting "Everything worked out fine.", like everyone else has done.
Keep us updated!