My wife and I are tossing it around if we should buy or not. We are thinking about purchasing the lowest tier(100 points). I would like to hear the pros and cons from those of you who purchased. How many years am i locked in for.
That depends on where you choose to make your home resort. Several of the properties' contracts end in 2042. SSR is 2054. AK 2057 and BLT 2060. VGF is longer than that. Why don't you do some research regarding resale? You could buy more than 100 points for the same or less money than buying direct through Disney. That is what we just did. Got 100 more points than we planned and spent $5k less than we budgeted.
The other thing to keep in mind with resale is that there is no "lowest tier" buy-in. If you just want to get your feet wet, you can find 25-100 point contracts on the resale market. As a resale buyer, the drawback to the small contracts is that they command a higher price

, they tend to sell within a day of listing (so you have to be ready to pounce!

), and the closing costs are higher per point that with a larger contract

.
On another thread that you started you asked about what happens to the points if you skip a year. Some
DVC owners actually buy with the idea of skipping year in mind. With a 50 point contract, you could take a 150 point trip by using banked, current and borrowed points all at once. Now, you would be using 3 years of points, so you would have infrequent visits that way, but some DVC'ers don't go multiple times a year, or even every year. You still would have your MF's due in January each of those 3 years, but currently that is only about $5/pt, so for a 50 pt contract, about $250.
As far as being locked in, it does depend on the home resort you buy into, as
timandjani indicated. But, if you want to get out, you can turn around and sell your contract on the resale market. As I said, the small contracts are a hot commodity, so if you bought a small contract, you generally would have no trouble unloading it. Of course, with reselling using a broker, you will pay a 10% commission and some other small fees.
Good luck learning more about purchasing DVC!