I would suggest you go over to the DVC forums. There is a planning forum where you can ask questions. There is also the rent/trade board where you can get an idea of what people are asking per point.
The number of points you would need are determined by: time of year (season), size of room (studio, 1 bdrm, 2 bdrm & view), and days of week (weekdays are less points than Friday/Saturday nights), and resort. You would need to look at the points chart to determine what you need and how many points it would "cost".
Are you 2 adults and 3 kids...how old are your kids? If they are young, and you can manage in a 1 bedroom, it will be a lot less points than a 2 bedroom.
It's a good option and you will pay a LOT less than if you paid for the accommodations. You just need to do your research.
