As far as the # of points you need, look at the points chart for a 2BR for the time you're most likely to go. You'll notice that Friday and Saturday nights are about 2X's the points for Sun-Thu, so factor in whether you plan to stay over a Fri and/or Sat. If you go every other year, divide in half, then bank or borrow to cover your needs.
As far as Resale vs. DVC, resale would be cheaper, but you have to get your own financing. You can also buy sold out resorts via resale too. OKW is the cheapest onsite WDW resale and has the lowest maintenance fees too. (We're going resale because you can get more points for the same amount of $.)
DVC offers financing, plus you don't have to make payments or pay maintenance fees until your building closes in May '05. They are currently offering points for $85 ($10 off) for SSR only w/150 point minimum. Closing costs are included and you don't have to worry about ROFR. My suggestion is that if you do NOT choose resale, then go ahead and buy SSR now, before the incentive shrinks or goes away.