It's hard to go wrong with the standard sized deck in the purple box, however, I would bypass Duquette's book. It is an attempt to 'dumb it down' for all those not bright enough to 'get it,' which is not only insulting, it only makes it more difficult when eventually confronted with the truth. To me, this book makes it painfully obvious that its author is one at least who doesn't get it.
Fear is compounded when it is coupled with the unknown. Why not just go straight to the source. Crowley's autobiography, The Confessions might be a good place to start, or The Great Beast by John Symonds. There are a few other good biographies available but most of them get the bulk of their information from the previous two sources. Then there is Crowley's The Book of Thoth itself. While it might take longer to work through books like these, in the end you will be much more richly rewarded than by taking the easy way with something like Duquette's book.