well i don't study either but i think Reiki is just healing energy while Ama Deus is more spiritual.
real witchcraft isn't like the movies, you can study multiple things [but i would study one at a time] you just might find you prefer one over the other, so you focus on one path over the other. you'll still know both [or as far as you got in one] you just prefer doing one type of healing. you're not forced to follow something you don't like because you said yes. it's wise to think before making an oath, but deciding to buy a book on both, or taking a few beginners classes doesn't equal a lifetime commitment.