There is zero reason to get a Wii U without a gamepad. I believe you need one in order to set it up, but that's the primary selling point of the console. I am not sure if the power brick will work between Wii and Wii U, either.
Otherwise, your Wii peripherals will work. You can use any HDMI cable, Wiimote, and the sensor bar is the same.
"A life is like a garden. Perfect moments can be had, but not preserved, except in memory. LLAP"
-RIP Leonard Nimoy