DuQuette's explanation of this pesky tzaddi business is easy to understand and makes sense. His book and Snuffin's make the Thoth more accessible without dumbing it down.
And while I don't know the book about the decans, I think a good working knowledge of the basic astrological terminology helps, and so does an understanding of each planet's and star sign's characteristics. Once you "know" Saturn or Venus and how they influence their surroundings, you can think for yourself what happens when they're in Cancer or Taurus. Add the number (i.e., the placement on the Tree of Life), and you have a pretty good idea of what's going on in a card. Seeing it depicted in the wonderfully complex but nevertheless coherent images of Frieda Harris is even better when you know how the planets wander through the signs, and together, they land on the Tree of Life's sphirot.
I think the Thoth is a great reading AND studying deck.
One more thing: it's fun and instructive to take out all the Saturn-influenced minors, all those under Jupiter's influence etc. Decan groups. Compare, find what they have in common, what not. It's a great addition to the easily visible elemental association of the suits - everybody knows that Swords is either Gemini or Libra or Aquarius. But seeing how the planetary influences play out just by looking at the cards is great.
I also put from time to time the minors on my study Tree of Life, sorted by numbers, just to get a better feeling for the connection between sphira and number.
As I said, Thoth is a studying tool of the first order.