As for controllers how it works is:
You can use a Wii Mote on a Wii U system, along with other Wii attachments such as the Nunchuk, Classic or Classic Pro that attaches to the bottom of the Wii Mote. This allows you to even navigate the Wii and Wii U menus with the analog stick. Be aware though that the Wii U emulates a Wii and will not be compatible with Wii U specific accessories for controlling purposes, including the Wii U gamepad while in Wii Mode. That means that for any Wii games you decided to play, say with your gf, you won't be able to use the Wii U gamepad as a controller and you will need two Wii motes for multiplayer Wii games.
That being said, the Wii U gamepad does still stream audio and video while in Wii Mode. And as far as which attachment to use, most games require the Wii mote + Nunchuk, Classic or Classic Pro but are compatible with all of them so which to use is up to you. I prefer the Classic Pro for most games apart from the few I mentioned in the list.
Xenoblade is one of the best RPGs to come out in a while and once you play it you'll probably be thinking, "why don't they do this in MMOs?". Check it out.
And yep I do have MH3U so let me know when you get it and I'll add you and we can start fresh.