To get started, I would pick up…
For the adults: Okami (very long adventure game), Zack & Wiki (cheap and great!)
For everybody: Super Mario Galaxy, WarioWare: Smooth Moves, Tetris Party (downloadable), World of Goo (downloadable), then download some classics! Super Mario Bros. 1 & 3, old Zelda games.
Accessories: 1 or 2 extra remotes, 2 classic controllers. Nothing more!
WiiFit is fun, but you’ll tire of it fast. And you get Wii Sports for free! This stuff is all Grade-A, and tons of fun.