Hey Miles, welcome to the forum! I mostly practice the Gallery’s magick so feel free to PM me or tag me in a post if you have any questions. I’d try searching their blog posts or FAQs first though, they’ve probably already answered many of the questions you may have. There are several books-worth of material on their website, all for free.
The 72 angels book is a great one, and if you’re interested in calling on Raziel and other archangels, the book Archangels of Magick, also by Brand, is very very good as well. The Sigil Rituals in that book are actually much simpler than the method with the Shem angels in case you want to try something a bit easier to get you started. I still use the simple stuff myself, and it’s wonderful how effective it is.
Also, it sounds like you’re interested in understanding mystical secrets, not just purely practical work, but do not discount the more “material” or “mundane” magick. The greatest understanding comes from deep within the self, and one way of getting there is by uncovering and obtaining your true desires. Even the most base of magick can reveal profound truths about your self and about reality.
Embrace who you are, and with patience, you will find the answers you seek. Follow your intuition, trust in it, and you will be guided to a wondrous, magickal life.
Many blessings upon you friend