Siff’s Supertraining is amazingly comprehensive and already seems like it will be used over and over as a reference in my own training. As far as books for you to purchase, like some of the other (more experienced) posters have noted, you’d almost certainly be better off amassing a large library of knowledge be it from purchasing books or not. I find myself going off on tangents in my training related book purchases and hope that I’ve finally settled on some of the more useful literature available (from old school dogmatic football training books to “combine specialist” books, a few from Human Kinetics and now finally things from UAC like Supertraining and some of the Yessis books).
That being said I’m looking forward to getting myself a bit of disposable income and purchasing some of the Charlie Francis products. (GPP Essentials and Weights for Speed are on my wish list 
)