A Possible Scaled Back Plan
As others have noted, your original plan was a bit ambitious, especially for a first RoadTrip. However, it doesn't have to be cut back much to be something truly enjoyable, and more about seeing stuff all along the way rather than driving for days to get to some distant destination. If you set the Grand Canyon as your farthest goal, then you can make a very nice trip that would include stops at Tower View in Jacumba, the old Territorial Prison in Yuma, the former mining town of Jerome, Sinagua Culture ruins at Tuzigoot and Walnut Canyon National Monuments, Sedona and the scenic drive north on AZ-89A through Oak Creek Canyon, Sunset Crater and Wupatki National Monuments, Cameron Trading Post, the Grand Canyon, the largest remaining stretch of the highway formerly known as US-66 from Seligman through Peach Springs to Kingman, London Bridge in Lake Havasu City, the below sea level Salton Sea and Anza-Borrego Desert State Park. On second thought, you won't be able to visit all those stops, but such a circuit would only require about 2½ days of driving leaving you enough time to visit many of them at a relaxed pace.
AZBuck