Start with the originals--Torah, Bible, Koran, Vedas, Buddhist Canons, Greco-Roman Mythologies, Avesta, Enûma Eliš--then work your way out toward commentaries,

Start with the originals--Torah, Bible, Koran, Vedas, Buddhist Canons, Greco-Roman Mythologies, Avesta, Enûma Eliš--then work your way out toward commentaries, sects, cults, precursors, apocrypha, heresies, schisms, etc. The problem with any condensed "Grand Tour of Religion" is the inevitable editorial bias (i.e. adopting someone else's understanding instead of developing your own).