If you buy through resale, there is no minimum number of points to purchase -- you are just limited by what is for sale.
I also understand that if you buy through WDW there is no closing costs but I don't know what the costs are through resale.
When I posted a similar question on buy vs. resale, many kind members on this board gave me some great answers. See below -- the credit all goes to them!
From Chuck S:
There is no difference whether you buy SSR through resale or Disney, except:
1) Your resale offer will need to clear Disney Right of First Refusal.
2) It will probably take longer to close resale.
3) Disney financing is pretty easy to get.
4) It will take longer for you to get into the
DVC computer system, usually a week or so after closing. If you buy from Disney you are in the computer right away.
From BroganMc:
Resale contracts on the newer resorts tend not to give you a better deal than Disney. Older resorts, I suspect, are snapped up because people really want to stay there and tire of the 7-month frenzy for reservations.
Believe it or not, that extra 4 months of reservations at your home resort matters when you: need special accommodations (handicap rooms, cheaper studios, grand villas) or are going at high travel times (summer, spring break, Christmas, etc.). There are quirks to DVC you may not expect as well. For instance, when the Food & Wine Festival happens in October/November, it's hard to get a ressie for Beach Club and Boardwalk. And the first two weeks of December are high traffic for DisneyWorld DVCs because of the low point use and Christmas festivities.
From Wisbucky:
Another issue to keep in mind is if you buy from Disney you will have to purchase 150 points minimum. Resale you can purchase any amount of points. However as many have found out here you will become addicted after you buy your first rounds of points and most likely add on.
The best advice I have ever heard or actually listen to was buy where you want to stay
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Best of luck in your decision...we are still deciding ourselves.
Marsha