We figured out how many points we thought we'd need like this:
- we thought about how long we usually liked to stay (you don't have to stay a full week -- a one night stay is OK)
- we thought about how big of a room we'd need right now, how big of a room we'd need in 10 years, how big of a room we'd need in 20 years, etc....
- we thought about how often we liked to go
- we thought about how much we could afford
Then we realized that the 160 points minimum would not be nearly enough points for us and bought 220!

When we bought we got "developer points" which were a whole extra year of points that had to be used right away. We've used those, plus our 1st year's points, and half of our 2nd year's points. We'll use the 2nd half of our 2nd year's points in another 5 month's and then be borrowing from the 3rd year. So bottom line, we really could buy another 100 points.
Now our kids are 6 and 9. We are 39. Are we really going to use
DVC when they are in college, out of college, etc? Well, we went to
Disneyland a lot before we had kids, so I think so. You can bet that once they are old enough to wander about by themselves that you'll be able to find me in the spa at the Grand Cal at least one hot afternoon...especially when as I get further away from 39.

Once they start having kids, I know we'll want to take the grandkids & then we definitely won't have enough points again...sigh!
I'm in California, so I don't know about Florida rates on hotels. I know that in California, Disney has Annual Passholder rates on the hotels here.
You should also look at the resale market. If you are only looking at going for a weekend and don't need 160 points, you can buy a small contract by resale and try it out without buying the 160 points Disney wants you to buy to start out.
Good luck with your decisions!