the regular copy is released on October 4th (I assume this is just for the US copies, what date is for JP?).
October 4th is
US physical release
EU physical & eShop release
Jp's physical & eshop is released on September 24th.
Is the digital download bound to your Wii U console? Can I give it to my friends? Say I sell my Wii U, then buy a new Wii U months later. Do I then still own the game? Would I have to deactivate it on that Wii U console first so you can't multiply copies?
The digital copy is way more restricted than a Xbox 360.
For example if you want to bring the digital copy to your friends house who also has a Wii U, you need to bring your entire Wii U console. There is currently no as a Wii U to Wii U transfer.
Nintendo IDs are restricted to one console, so if you sell your own Wii U and bought a new one, there is a good chance that you have to rebuy the same product again.
Even IF the Japanese is faster, how do you obtain it?
The current method today is to import a JP Wii U and buy the JP copy of the game (physical/eShop).
If you digitally downloaded Windwaker HD, can you manually change the language settings?
No. All of the US copies have 1 language or probably 2 if Canadian French counts.
The European copies supports 5 languages that can be changed via Wii U settings, but no JP language.
However, during the introduction to the game, the caster explained that you can use a regular controller for the game instead. Can we use a GameCube controller?
The Gamecube controller is not compatible for Wii U games as it lacks Gamecube controller ports. There is an accessory that enables you to use GC controllers but only for games that uses the Wii Classic Controller (think of Smash Bros Brawl, & Virtual Console).
The only controllers compatible are Wii U Gamepad and Wii U Pro Controller. IF it supports Wii Classic Controller then there is a chance you can use the Gamecube Controller.
Just wanted to note that if the auction house works as it does in The Windwaker GameCube, the fast sail may be randomized with the treasure chart, piece of heart, etc. I do hope it doesn't come to a reset point when you have to obtain that -- it would be very unfortunate.
The Fast Sail requires at least 101 Rupees minimum if you are really lucky. Probably ~180-220 rupees when trying to win the auction.