If you buy the 50 point resale you are then a DVC memeber. You can add on either 25 if you do not need to finance or a minimum of 50 if you do need to finance from DVC.
We just bought a resale at OKW for 25 points. I chose it over a 50 point + contract because I decided it was something I could easily pay cash for and then at anytime I can add another contract, probably at BCV, and pay cash again. Plus, you can always add points you have transfered from another member. I felt like it gave me the most flexibility possible for the lowest commitment.
If you own a DVC contract, you are a member and will have access to all DVC programs and perks. The only limitations will be created by the number of points you will have to use. With banking and borrowing, you will have access to triple your allotment of points. With a 25 point purchase, you would have a maximum of 75 points every three years.
The minimum of 150 points applies only to purchases thru DVC. Ownership of as few as 25 (that's the smallest contract size possible) will still make you a DVC member.
Once you buy a contract you are a member. Unlike other programs there are no differences among mnembers based on how or where they purchased the contract.
Initial contracts purchased from Disney for new members are 150 point minimum. After that you can purchase any number of points from 25 up to your resort or overall maximum. If you want to finance points purchased from Disney the minimum add-on is 50 points.
But perks are not guaranteed and may disappear at any time. Like The Disney Store discount. The AP discount might only be for this year. If you buy into DVC just for the perks/discounts, you still have to pay your dues until 2042 or 2054 depending on where you buy.