I just bought a Wii-U, it's due to arrive Monday, and this is the first game I am going to get. I am just wondering how the multiplayer is going to work as I wanted to play co-op with my girlfriend.

Well, yes. You might be way more comfortable with the Pro controller. But you only need to buy 1 pro, and you can use the Wii U pad you already have. I doubt I'm wrong.

The game supports the Wii U gamepad, WIi U Pro controllers, and the Wii remote+nunchuck.

I hope it's not like the 2D Mario where you could only use the wii u controller for multiplayer to place blocks.

no classic controller? D:

It supports literally any Wii or Wii U controller I believe: Wiimote, Wiimote with nunchuck, Pro, or Classic. Maybe not the balance board... ;) The e-manual lists all the button changes. You do need the gamepad for some things e.g. Toad's puzzle levels for camera control, blowing on the mic (lol), and so on. Nintendo usually goes to great lengths for multiplayer titles to make it pretty likely you can scrape together enough controllers for everyone.

So we can use the gamepad along with another controller such as pro controller instead of that stupid 1st player placing blocks stuff?

Player 1 will be Gamepad. Player 2 can be Wii U Pro Controller, Wii Remote, Wii Classic Controller, or Wii Remote + Nunchuck.

Any controller you can use with the Wii U you can use with Super Mario 3D World.

I wasn't aware of a 'Pro Controller', as all I got 1 year 6 months ago when I first bought my Wii U was the games machine and gamepad. You can also link in multiplayer mode by using your old Wii controllers/nunchucks - but if you never bought the previous Wii the Pro Controller is the better option, especially like with mine if it's not included in the package.

I'm saving to get the Mariokart 8 game. :)

At the moment, there are no games that support multiple Wii U tablet controllers. Using a tablet controller is optional for both single-player and multi-player but you do miss out on a handful of levels in single-player. You can choose to use Wii Remotes + Nunchuck, Wii U Pro Controller or the Wii Classic Controller Pro.

Edit:

y u bump dis?