What would be some good reading material?

There are many small introductory books by our spiritual master, His Divine Grace, A.C. Bhaktivedanta Swami Prabhupada, you will like them. Some of my favorites are, “Perfect Questions, Perfect Answers”, “The Science of Self Realization”, “Beyond Birth and Death”, and many others. You can also read the articles on this web site.
The main book is the Bhagavad-gita, but be careful to get Srila Prabhupada’s “Bhagavad-gita As It Is”, there are many translations, but the special quality of Srila Prabhupada’s Bhagavad-gita is he has presented it “As It Is”. He has not added anything new or changed the meaning of the verses as almost all the other translators have done.

Do you believe in one all-powerful being?

Yes. Krishna — The Supreme Personality of Godhead