It really pays to read, read, and read more and really do your homework before you even consider putting a deposit down either directly with Disney or via a re-sale broker.
Best place to start the
Point Charts for DVC Resorts ( link is at upper right corner of this page under The Timeshare Store Banner ) - get better idea of how many points you'd need to get started in DVC by doing lots of calculating :
what days of week & how many days total you'd vacation AND
which resort(s) you'd most like to stay at (always pick your favorite to purchase all or most of your points at ) AND
size villa you'd need
AND don't forget to take into consideration the various travel seasons you may want to book.
A family of 4 especially with older kids, jmho needs at least 1 bedroom villa. Note that at AKV's Kidani DVC building & at BLT all 1 bedroom villas will have the bonus of 2 full bathrooms and a pullout sleeper chair that sleeps 1 in addition to pullout sofa that sleeps 2 ( all 1 bedroom villas have king bed in master bedroom at all DVCs). AKV you will find available via re-sale but BLT will probably be tough to find on re-sale for the near future at least.
Its best to purchase points at DVC resort you'd like BEST ("Home Resort") so you know you will have 11 month priority booking advantage there ( at 7 months or less you can use your points to book at any of the other DVC resorts ). Also take into consideration annual Maintenance Fees which presently range from $3.67 at BLT to more than $6 per point at Vero Beach Resort; the Home Resort your points are from determines what your MFs will be each year - that amount is multiplied per point to give total amount you owe on MFs each year.
Some people also take into consideration the length of contracts at the various DVC Resorts when deciding which resort to pick for their Home Resort; these are the expiration dates -
BLT 2060
AKV 2057 & OKW "Extended Contracts" 2057 - note that all OKW sold by Disney are extended contracts but resale OKW may or may not be an extended contract
SSR 2054
BCV, BWV, VWL, & OKW "Un-extended Contracts" 2042
and offsite DVCs Vero Beach & Hilton Head Island 2042
You mention starting off with a small re-sale but wonder what you can do with a small contract :
you can bank one year's allotment of points into next year to have 2 yrs worth of points to use every two years and can also bank one year's points into next & borrow from the upcoming year to have 3 yrs worth of points to use every third year so it is possible to start off small via resale and still have the ability to work with that until you are ready to do future add-on(s) for additional points.Best wishes and hope you find the contract that best suits your needs