Thanks, TarotBear. That's my uneducated sense of it at the moment. And I don't, at this time, want to overwhelm myself with yet another exhaustive list of "meanings," especially if they don't have direct relevance to Tarot.
What, in your opinion, is a good way to study/understand that branch of Numerology that's connected with Tarot (Qabalah?)?
If you study Qabalah in conjunction with Tarot, it'll come to you in time, as Qabalah is essentially Pythagorean numerology glorified. From a cursory look at the Wikipedia article, it is striking how common interpretations of the single-digit numbers correlate to philosophies behind the Sephiroth.
https://en.wikipedia.org/wiki/Numerology
You're already reading Dion Fortune's book, I also recommend Robert Wang's book. Since you seem to be in a quandary about which direction to take, based on this and other posts, I can only recommend the way I study it. I began with DuQuette's Chicken Qabalah, studying it (actually paraphrasing practically the whole thing in my notebook) then doing the same with Wang (which I found interesting, but rather dry) and Fortune. After I had what seemed to be a good base, I began an in-depth study of the Thoth with the Book of Thoth. Going slowly, making sure I don't skip anything until I understand it, I analyze the path's place on the Tree, symbols, parallel paths, other paths that have significance to it, opening and closing Sephiroth, the meaning of the Hebrew letter, astrological attribution, initiatory significance and (unique to the Thoth) Thelemic connection (including what cross references I can find in Crowley's corpus).
I don't even study astrology per se, since it doesn't interest me that much, but the stories behind the signs and planets. I pick up things like rulers and exalters as I go along, as they make very interesting connections between the paths and Sephiroth. Since everything is interconnected, this actually makes the whole thing easier.
It's going slowly, sometimes taking a month or more for a single card, but very enjoyable. After about a year and a half of study, I'm at the Hermit. Learn the meanings of the letters first, basic Sephirotic definitions and take it from there. Don't even try to memorize things; going card by card and path and using the same set of tools over and over, you'll find that in time you remember things of your own accord. Just don't be impatient, do it for its own sake and you'll be fine. My advantage is that I work as a graveyard shift security guard, so I have the luxury or spending about three to four hours a day on the whole thing (any more and my brain turns to mush) but taking it on your own time, you'll be able to reach great results nonetheless.
I've been known to move a little too quickly.