It occurs to me that it’s very hard to take the first steps in orienting yourself around SIM because outside of Chris Warnock’s courses there is nothing really like a 101 book. I’ve attempted to do some of that with my lectures, but there’s only so much you can do in a narrow window of time.
Even more important is orienting oneself towards the worldview of pracitioners of the system. Thinking like someone in the 21st Century rather than someone in the 17th is a major stumbling block, because so many assumptions about the self, the universe, and metaphysics overall have changed that really do matter. There is much to un-learn before you learn.
Chris requires one of two books early on in his Astrological Magic Course. The first is The Elizabethan World Picture by E.M.W.Tillyard. It’s a very useful book, but one of the most boring I’ve ever read.
The better option is The Discarded Image by C.S.Lewis. This book I can wholeheartedly recommend, and convinced me that the pious Lewis almost certaintly practiced some form of Christian Neoplatonic magic in secret.
I’d like to go a bit further and add two more books to your reading list, one of which is much easier to obtain than the other.
The first is the Timaeus of Plato and the many, many commentaries upon it. A great deal of the justification and rationale for (Traditional) astrology in Western Culture originates in this text, and it is profound elegant reading if sometimes a bit dry. You should read it fully at least once, but it certainly grows in value upon subsequent reads.
The second is De Radiis Stellarum of Al-Kindi in French and a harder to obtain version in English. Though this text was certainly respected in the Muslim world, it was widely disseminated throughout the Christian medieval world as an explanation for magic which did not recourse to the evocation of demons and only mysterious natural forces. More relevantly, it’s a logical philosophical and integrated view of how magic works and much more sophisticated than anything which has emerged since. Without understanding De Radiis Stellarum, it’s actually very hard to understand Picatrix; and it happens to be one of the biggest skeleton keys to understanding the text for my own researches.