Crowley's Book of Thoth, to go with the first deck I bought, that being a large Thoth in 1983. (Yes, I threw myself into the deep end with a cast-iron life vest!)
Definitely! You're a brave soul!
I thought I posted in this one, but I haven't yet, so here goes. In the pre-Amazon, pre-internet days, I had 3 books:
Pictorial Key. My reaction at the time: "What the heck!? I'm an English major--I KNOW I can read--but I'm having some trouble with this . . ."
Eileen Connolly's
Tarot: A New Handbook for the Apprentice. A good workbook that helped me start thinking for myself, not just memorizing meanings and reading pictures.
The Motherpeace Tarot Playbook. Opened the first drawer of tarot as the esoteric filing cabinet for me, for astrology and chakras, especially. Very helpful for a beginner. I still use some of its non-RWS interpretations regularly because they clicked with me back then.