Just when you think you have enough..they pull you in w/incentives!
Initially we got we thought we would need to give us 5-7 days/yr. (170)for our 1 trip to WDW. Well, we have since added on 2 small add ons for various reasons. (Kids get older, need more space, in-laws travel with us, wanting 11 month option at certain resorts).
So I would suggest start with what you would need for the time of yr., the unit size(studio, 1br, 2br) and # of days that you plan to stay in your home away from home. I agree w/ "chunks" of points instead of one big point purchase.