Jay, this sounds like a bucket list type of vacation. Route 66 offers loads of information via the internet. With 4 months of prep time you should be a able to plot out the perfect itinerary. When I have time during the next couple of days I will provide you with some suggestions starting around Flagstaff AZ. The time you have picked is very good, the weather will be mild and the camp grounds will not yet be full. My only concern is the amount of time you have allocated for such a long trip, you might be able to complete the loop but I doubt you will have any time to stop and smell the roses.