Unfortunately, I don't think there is a single comprehensive walkthrough on how to make a Wii portable. But, honestly, if you need a walkthrough, you should probably start with someone a little simpler, like a SNES portable/NES portable.
The problem with any step-by-step detailed guide is that it is by definition very specific and therefore of limited use should you deviate in the slightest from plans. Take Ben's book. Everything is labeled with letters that connect to other letters- there is little to nothing on what each thing actually does. This is especially bad with the NES part IIRC.