BivalentZs

I bought a Wii U a few months ago. I set it up by creating a user and linking it to my eshop and all that fun stuff. Got all set to enjoy my Wii U.
Then I saw Nintendo was releasing the Limited Edition Zelda Windwaker HD Wii U. Being a huge Zelda fan. I had to have this new Zelda Wii U.
Today I got my Zelda Wii U and started the process of selling my old one. First things first was deleting and restoring the old one to new factory settings.
I went to do so and it mentioned something about my user and Id being permanently linked to this system. Now I'm nervous if I sell it the new owner can access my account and downloads. Also when I set up my new Wii U can I access my old account anymore? What do I do to be able to make the transfer as easy as possible with the least amount of headaches? Suggestions? Tips?