I am a fan of the transpose button (used to change keys that you're playing). For example, you can play Amazing Grace in the key of C and use the transpose button to the key of F so your voice can reach all the notes.

This is the EXPRESS way to learn keyboard skill. Just concentrate in the key of C which is the easiest because then you can avoid all the "black" notes (or minimize them). This way, you can learn all the basic chord progression and rhythms. These are the essence of keyboard playing and develops your fingering (piano skill) and sense. Soon, you will be playing at the pro level without worrying too much about the key. You can pick up that skill later after you master the keyboard essentials.

Using the auto accompaniment is also helpful but nothing replaces piano playing skills with your hands for comping.