I want to walk the full length of the wall, where can I find the info to get the necessary permits?

Eric, there is no specific permit. To enter mainland China, a visa is fine. However, some sections of the walls are close to the military restricted areas. So you can't go there. What's more, you should understand that some sections are ruined and disconnected since they were built long ago. So it's difficult to take a full length tour of the wall. I think you might pick up some representative parts for a visit, such as Badaling, Mutianyu, Jinshanling and Simatai.