You can spend hours trying to figure out how many points you will need to purchase, but this also includes trying to figure out your vacation needs years from now...not an easy task. As a general rule most studios cost about 18-20 points per night so if you are looking for 7 nights then you will need 140 points(annually) for a weeks vacation at WDW. A 1-bdrm will cost you double or about 280 points.
If your plans are to stay over the Xmas holidays then add a 75% premium on those point rates.
We have 150 points but we seldom visit over holiday or school vacation periods so we can stretch our points to over 10 days annually or bank and borrow for a 7 day 1-bdrm visit.