You can buy
DVC two ways. You can go through Disney direct or buy a contract via resale.
Through Disney, they do have a minimum It used to be 160 but was lowered in the late Spring down to 100 for most resorts. In some cases, people were allowed to buy in with just 50 points.
Whether that is still allowed or not, I do not know. If you buy resale, the number of points will be determined by the contract you choose.
The price varies by resort and where you buy. Disney is more expensive than resale but some of the newer resorts are not as easy to come by on the resale market and your options are limited.
What I would do is first try to figure out when you want to travel to Disney, in what type of room, and about how many points that is. Then research the different resort options so you can choose a home resort you are comfortable with.
While you can trade out to all the DVC resorts at the 7 month mark, you want to own a place that you would be okay staying if what you want at the other resorts are not available. Many members book their home resort at 11 months, just to secure a reservation for this very reason.
We own at BLT because that is where we want to stay. We have tried BWV, VWL, and BCV but BLT remains our favorite. We bought through Disney and paid more than we would have had we bought one of the less expensive resorts like SSR or OKW. However, we have no desire to stay at those resorts and felt it was worth spending more to know we will be at our top choice all the time.
Good luck!