You will be rolling right along to do all of it but I understand time restraints. We did the trip a few years ago but we stayed a bit longer. I do know that staying in Williams Az at the KOA was a good choice for us. The Grand Canyon railroad leaves from there and we enjoyed doing that a lot. If my memory serves me correctly it is about a 40 minute drive from Williams to the Canyon. For us the KOA was centrally located more or less from what we wanted to do. I am sure where you have picked is more central for you too.