1. Do Rim to Rim to Rim in two days. It's easier logistically and not that hard to go back the next day assuming you're in shape.
Or three days with the middle day spent lounging around and enjoying views of the canyon.
I was going to do the rim-to-rim once but learned that the bus ride back was going to be long and kind of expensive (for me at the time). A sleeping bag, bivy sack, pad, food, a few other items isn't that heavy.
At the time there was a walk-in campground on the north side that required no reservation (for hikers and bikers). Is this still the case?