(1) Yes, you can get the Zelda pack, for example. You can get the 'player's choice' pack at Walmart and choose between a variety of games.
(2) There are tons of great games. I just got a DS in December and already have 11 games. i'm currently playing Simcity (which I *love*) and Zelda, but Elite Beat Agents if you like beat games, New Super Mario Brothers if you like platformers, Mario Kart DS if you like racers, etc are all amazing games. The DS is the best system for gaming right now, and it has a pile of RPGs already out and a pile more coming.
(3) Yep. It doesn't build on wind waker at all, although it uses a similar art style and you have a boat. However, you don't spend nearly as much time at sea as wind waker.
It's also worth noting that there are tons of great games that have become bargain priced. You can get many DS games for $20 or less, occationally finding good deals for $9-$13 -- Elite Beat Agents was recently available for $10, for example, and it's normally $35. Stores sometimes have "buy any 2 of the following DS games for $20 total" deals, and there are often bins full of bargain priced DS games at stores.
It is just a very fun little system with tons of great games and interesting new gameplay due to the stylus. The stylus is closer to a mouse in behavior, so a lot of computer games (Simcity, Myst) can get ported easily.
