I Will Be Backpacking The Grand Canyon Rim-to-rim Route. Just How Difficult Is The Trip?

The rim-to-rim hike is one of the premier backpacking destinations in North America. While it sounds arduous, having hiked it twice, I'd actually rate it as a good choice for beginners.
First, the trail is all switchbacks and very well-maintained. All sites in the four campgrounds are assigned. All have running water and outhouses, and Phantom Ranch even has a restaurant and electricity. Hardly a very tough backpack trip!
Hiking back up from the Colorado River to the south Rim strikes fear in many people's hearts. But the trail is properly switchbacked, and you break up the approximately 10-mile distance with an overnight at the Indian Gardens Campground.
Finally, there is a shuttle from the South Rim back to the vehicle you left at the North Rim trail head.
The hike starts on the North Rim, 6,000 feet above the canyon floor and 1,000 feet higher than the South Rim. You start out in dense ponderosa pines and among aspens, which  turn a pretty gold in fall. The canyon bottom is classic high-elevation desert with scrub and cacti. The hike up to the South Rim is more barren because of increased solar exposure. But creeks lined with cottonwoods make the hiking and campgrounds pleasant and cool.