Hiking; am I in good enough shape?

Simple answer; yes.  There are walks/hikes for every fitness level.  The Rim Trail, which follows the edge of the Grand Canyon is paved.  There are few uphill sections, and can be as short/long as you feel comfortable.  Keep in mind, the South Rim is at 7,500 feet in elevation (almost 1.5 miles).  The air is a bit thin, so you will get fatigued quicker.