I would make a few suggestions:
1) If location is important to you , then buy at the resort you want to stay at since you can book that 11 months before your vacation.
2) If location does NOT matter and you do not mine staying at SSR or OKW most of the time, buy where ever is cheapest.
3) Take a good look at how many points you need based on a) when you usually travel, b) accomodations (Studio, 1 BRM, 2BR) c) resort d) possibly view type. with 6 kids. I would guess you are looking at 2 BR or Grand Villas. I suggest not going over what you think you will need. You can purchase 25 additional points at $15 from
DVC within your UY(they are only good for one year). So if you ever need more, you eitehr borrow or pay for a few more one time use points.
4) Ideally, get a UY that is just before your normal travel. If you typically go in August, a June UY would be best. That way if you HAVE to cancel, you have plenty of time to bank / rent your points.
5) Since you state you are looking at resale, the ideal contract has points banked from the previuos UY though you MIGHT pay a bit more for them. But that would allow you to vacation on banked points and continue to do that. If you ever want to go on a big vacation, you could simply pull 2 or 3 years of points (banked, current and borrowed).